Is a DTAC simcard which I buy at 7-11 as good as a simcard which I buy at one of their offices?

I will be able to extend the validity to almost a year? Or is it better to buy a simcard at their offices, for whatever reason?

Technically the SIMs are functionally equal (at least per provider/currently sold).

It's just a piece of electronics from the SIM card manufacturers (with a unique hack proof serial nr.).

Then comes the provider and binds the SIM to one of his (many) tariff packages (registered in the providers database).

Here in Thailand they tend to make a fuss about numerous different pre-packaged SIMs in nice carton/envelopes.

Maximum confusion

These packages can easily be changed due to your needs (about anytime after purchase, costs a fee usually).

(another poster mentioned a smartphone app from DTAC to manage that).

There is no "quality" difference between SIMs purchased at 7/11 or DTAC office.

The SIM has to be registered to your name (bring passport).

DTAC "package selector":

(select "Prepaid")

https://www.dtac.co.th/en/home.html

Depending on your device/phone the (full size) SIM has to be cut down ("micro SIM", "nano SIM").

A job easily done at almost all phone booths.

Don't know whether they do it at 7/11?

So I can also register my sim card at 7-11, just like they do at the offices?

It was possible last year.

I haven't dealt with that for long.

A friend registered a new SIM at a Bangkok 7-11 last week. Needed passport, took less than 2 minutes.

You should be able to buy and register a Happy SIM card and nearly any 7-11 however, I have not had much luck lately. I went to four different 7-11s. They either could not register sims or they did not have stock of the standard 49baht cards. Had several other specialty cards, 4G internet cards, etc but not the simple standard SIM that I wanted. I found it easier to just visit the DTAC shop at Central Mall here in Pattaya, gave them my passport and they had me in and out in a jiffy.