To continue your analogy, you are changing your car for the same make and model just a newer version, there is no reason to suspect the new car cannot seat the same number of people as the old one , but you want the actual dimensions of the seats ,
Is it not reasonable to just plug your devices in with a multiway adaptor and see if they still ring?
If you need more wired phones than supported, use a digital voice adaptor to connect them.
Given most people using DV will have DECT handsets, the multi phone capability of the Smart Hub 2 phone socket is a, well, ‘niche’ interest. If you use multiple DECT Handsets then you can actually make more than one call at once on a number - something you cannot do with a load of old handsets connected to the same port on the smart hub.
I was an apprentice at the time, but REN (Ringer Equivalent Number) numbers came into existence when PO Telephones first allowed people to connect their own devices to the network - part of the introduction of sockets (circa late '70s early 80's), rather than hard wired phones. Phones back then had a bell set and associated coils to operate it, and the the bell circuit was wired in series, whereas phones are in parallel. Due to the current drain of the bell sets, it was determined that a max of 4 (I think) was all that was permitted, due to the power drop in each bell set.
Modern devices do not use the bell circuit - they just sense the incoming ringing current, then electronically make a ringing noise, so then REN number is now totally superfluous and you can have as many devices connected as you like.
Unless you are a fan of old school handsets of course (although they would still need to be DTMF as loop disconnect is no longer supported).
(Ah yes, I remember when there was that limit. Eg my father, a doctor, had a phone by the bed for night calls and one downstairs in the 60s and that was quite rare that we had two phones in the house. Then suddenly there were no restrictions and I ended up here with 4 upstairs and 3 down - 7 different rooms (until I culled it down to phones just in one room last Autumn in anticipation for end of 2023 digital voice which (thank God) has still not happened in this bit of London).
If REN was only relevant to telephones with bells, how come even modern corded models (still on sale, such as the BT Decor 2200) still display "REN: 1" on the base?
@Tim123 When the REN concept was introduced, the value of 1 was the lowest allocated. That remains the case today irrespective of the actual current demand of the particular telephone.
Further detail on current demand here: https://bt-digital-voice.blogspot.com/p/bt-smart-hub-2.html