Yes, grocery loyalty cards amass an inordinate amount of data on its users based on frequency and nature of use. It's interesting how the lower ticket loyalty schemes (grocery stores, etc) have arguably more powerful info than the higher-end types (air mile clubs, etc) for this reason; you can get more insight on a granular level.

I always lose my loyalty card from time to time (it doesn't have any loyalty advantages you just have to have it to get the discounts) and ask for a new one. I wonder if they were able to link them back together

Unless you always pay cash - it should be trivial to link by the payment card number.

Do they actually see a card number? Anyway, I have a couple and I have a habit of losing/breaking those as well. I'm just really bad at holding on to cards it seems

I always switch my loyalty cards with random people I meet on the subway, etc.

I always just use the phone number approach -- give them <local-area-code> 867-5309 an when they ask "yeah, I'm Jenny". Works every time. Last time at the Walgreens they tried to give me a $5 discount but I had to know the zip code assigned to the account so was like "nah, next time."

Ooh, I never thought of that, but now I am very very excited about it myself.

But the answer you get might be less exciting. They might say: "We know you bought A, B, and C".

What if they give you only part of what they know? How would you be able to tell if they know more? And even if you could, how would you convince authorities that something is wrong?

Also, they may have data that they just didn't "mine" yet. This may be data that they simply can't give you because it may concern you AND other people.

If you are in the UK, you can already ask for the information under the DPA.

But they could charge you a reasonable fee before. Now it will be free!

I would assume that he has all the data on you, you ever gave him. What else did you do expect when you signed up for the loyalty program?

> him

I think we're probably talking about national chains here.

I would imagine stores will use the loyalty cards to profile users, and if they've every stored any of the profiling data then this data will be the data you will be getting.