40 songs on 2 records?

30 minutes per side is certainly possible. And older songs were MUCH shorter than more current songs. The 50's era and before songs were often under three minutes. So ten per side under 30 minutes.. no problem.
Stating in the 1960's with the rise of LPs instead of 45's for popular music, then songs started getting longer.
(also, older songs have far less dynamic range (especially in the bass) and so need less 'space' between tracing the groove when cutting the master for LPs. The low freq. is where the space is needed for cuttinng an LP.)
So ten songs per side is easy. The limit seemed to be Beethoven's Ninth. Seemed they could just NOt fit it on one LP. The CD was designed to hold Beethoven's Ninth symphony!! So 70 minutes or 35 minutes a side was a streach too far on 12" vinyl

i just played a record with 25 songs

That makes sense thanks!

I remember a sticker on "Get Happy!" a fabulous early '80s record by Elvis Costello and The Attractions, boasting that the record contained "20 Hits! 20!" (Or something quite like that.)
Yup. Ten per side of vinyl. Many of 'em, most of 'em, actually, were quite short, obviously.

If you compress the dynamics it could fit even more!

I never buy those "best of" albums. They usually compress the dynamic range (or kill the bass) just to get more songs on the album. The customer thinks they're getting more for their money until they listen to it (and possibly compare it to a previous release that wasn't compressed).