Identity, data and measurement, from someone who runs it.
By Geetha Neelakantiah, SVP Business Development, Marketing & Operations, Semcasting
Welcome to the first issue. Every week: one story that matters, a few quick hits, one concept explained in plain English, and a reader question. I work at an identity company, so I have a point of view. When it shows up, I'll label it. Everything else is written to be useful whether or not you ever buy anything from anyone.
This week: Apple quietly shut a major DSP out of Safari, and it's a bigger lesson than it looks.
What happened. iOS 27 shipped on September 14 with an expanded Safari blocklist. It added identity domains you'd expect Apple to target: UID2, ID5, LiveRamp, Permutive and Audigent. It also added adsrvr.org, which The Trade Desk says is its core ad request and delivery domain, not an identity domain. The result, per AdExchanger: TTD can't serve ads in Safari on updated Apple devices. TTD filed a bug report with Apple's WebKit team; as of Monday, Apple was still reviewing it with no fix or ETA.
What it changes. Two things, and only one is about The Trade Desk.
What to do this week.
My bias, stated plainly. I work at a company built on deterministic identity resolved from first-party and offline data rather than browser cookies. So yes, I think identity that lives server-side is sturdier than identity that lives in a browser someone else controls. You don't have to agree with where I work to agree with the principle: don't let one browser setting be a single point of failure for your reach or your measurement.
New Jersey may have just made you a data broker. NJ's data broker law, passed in June, adds a "data collector" category: any company that collects data directly and sells or licenses it onward, with no minimum threshold. "Sale" is broad enough to cover routine ad tech data sharing. Registration opens April 1, 2027, with annual fees from $5,000 up to $1.5 million depending on how many NJ consumers are involved. The state has signaled it may pause enforcement while lawmakers fix gaps, including the lack of any exemption for political and voter data, but the ban on selling sensitive data (health, precise location, biometrics) is already in effect. Do now: map where your data goes after it leaves you. AdExchanger
MMM tells you what happened. Lifesight wants to tell you what's next. Lifesight open-sourced Horizon, a forecasting tool that runs several models at once and blends the results, and sits beside whatever mix model you already use. The useful point for everyone: mix models get unreliable when you ask them about budgets or seasons they've never seen. If you're using last holiday's MMM to plan February, be careful. AdExchanger
Taboola launches its own identity layer. Realize ID stitches clicks, video views, scroll depth and conversions across Taboola's publisher network into one view of a likely buyer, and Taboola cites up to 2.4x better conversion efficiency. That number is Taboola's own. The bigger pattern: every platform with scale now wants its own identity graph, which means more walled gardens and harder cross-platform measurement. MarTech Edition
Every identity vendor uses one of these words, usually both. Here's what they actually mean.
Deterministic means two records are linked because they share a known fact. The same email address, the same logged-in account, the same verified postal address. Think of it as matching two documents because they have the same passport number.
Probabilistic means two records are linked because they look alike. Same device type, similar location patterns, overlapping browsing times, same IP address at night. Think of it as recognizing a friend from across the street by their walk and their coat. Usually right. Not always.
Why it matters this week. Many probabilistic methods lean on browser and device signals, the exact signals Apple keeps restricting. The tighter the browsers get, the more that trade-off shifts.
Three questions to ask any identity partner:
Neither approach is "right." Most real setups blend them. What matters is knowing which one you're relying on for which decision.
How we'd handle this week's news. Semcasting resolves identity deterministically, server-side, from first-party and offline data rather than browser cookies or third-party ID domains. That means a Safari blocklist change doesn't touch how our audiences are built or matched. If you're not sure how much of your targeting depends on browser signals, we're happy to walk through your setup with you. Talk to us →
This month's spotlight: Open Enrollment
The busiest season in health insurance marketing is here. Medicare's Annual Enrollment Period runs October 15 to December 7, and ACA Marketplace enrollment opens November 1. Insurers and brokers have a short window, and shoppers in each channel need a different message.
Semcasting's Open Enrollment audience briefs cover all five channels:
Each brief shows qualified reach, fit tiers, the audience profile and the search themes those shoppers use. Audiences are scored for fit and measured weekly, so you can shift budget toward the channels that are converting while the window is still open.
Get the briefs: Open Enrollment Audience Briefs → · Questions: audience@semcasting.com
Coming up in future issues: Healthcare & Pharma, Financial Services, Political & Advocacy, B2B, and CTV.
"Our vendor reports a 70% match rate. Is that good?"
It depends on what they matched against and how. A match rate only tells you how many of your records found a partner, not whether the partner was right. Ask for the linking method (see the explainer above), ask whether they've tested accuracy against a known truth set, and ask what the rate looks like on your hardest segment, not your cleanest file. A lower rate with verified accuracy usually beats a high rate you can't audit.
Send me your question. Reply to this newsletter or comment on the LinkedIn post. Anything on identity, data, or measurement is fair game, including "is this vendor claim real?"
See you next week,
Geetha
Match Rate is written by Geetha Neelakantiah, SVP at Semcasting, a deterministic identity resolution and audience data company. Semcasting builds audiences, resolves identity and measures outcomes for brands and agencies in healthcare, pharma, financial services, political and B2B. Talk to us →