This isn’t an office building, and nobody “hid extra pairs in the wall” for good reason. This wiring is a very specific technique used to quickly feed phone pairs in new SFH and apartment buildings of a certain era when the minor CAPEX advantage of a single shared cable over home runs was sold to developers as a cost cutting measure (or just done anyway to pad wallets when home runs were specified).

You’re definitely right that it uses standard 25-pair color code, but it’s just a six pair residential run here: white from blue to slate, and red-blue.

I’m only seeing 6 pairs here. And, as I recall, 8 pair ewire is not a thing. 6-12-25 are the standard sizes for single binder in-home wiring of the era.

Little high on that pair count, look again. 😉

The term you are looking for for this wiring is “ewire”. In this case, it looks like 6 pair of daisy chained ewire.

It’s slightly twisted, but not quite up to being called CAT 3. Almost certainly nailed down along it’s pathway, and unsuitable as pull wire for anything more modern.

You could throw tone over a pair, then selectively snip/reconnect at each outlet to map the physical route… but again, it’s unlikely that will serve a purpose these days.

Because of the daisy chain, using a paired copper networking medium like DSL or G.Hn for these runs will not result in decent reliable performance either (at least without a lot of work turning them into home runs).

Best bet is to put the wall plate on, tie it into your VOIP line or home intercom at the demarc, and run fresh copper (or fiber where appropriate) to each room.

Wrong. Just… so wrong.