I’d agree names like Elizabeth and Sarah, Micheal, James etc are classics because they have always been in the top 100 names and have been consistently popular with every age.
Although I do think some people call a lot of names classic that shouldn’t be…on the this Mumsnet specifically there's a lot of different names that I see this happening with but for an example I see many ppl calling the name Emily a classic or timeless but that dosent make sense to me at all it didn’t enter the top 100 names until the late 70s and was the number 1 name in the US for 12 years in the 90s/2000s and number 1 over here for a few years around the same time.
And is already nearly out of the top 20, my dd was born in 2003 when the name Emily was at its peak and she had 5 in her year group at one point, if I heard the name Emily I’d assume it was someone born 20 years ago because that’s when it was popular. To me a name is a classic if it’s never been number 1 but always been there. Any name that is a “top name” at some point will always be associated with the generation.
I think those words get thrown around too much when people don't actually realise the statistics of some of the names they are calling "timeless"