I found the construction 数+counter before 何+counter+か which is on Bunpro but I can’t seem to find any information on the difference between them.
For example, what is the difference between:
数年 vs 何年か
Is it like 何年か is 2 to 3 years but 数年 is 3 to 9 years?
Don’t quote me on this, but the way I understand it is:
数年 - number of years, several years
何年か - some years (some number of years)
It’s difficult to express this in English, but my native language has the same distinction like Japanese, so while meaning is the same, the nuance is very difference. In one case you just say “several years” while in other you say “unknown number of years” or “some number of years” (actual number is unimportant).
But it’s probably better if someone who knows what they are talking about answers this as well 
I sort of understand I think. So 数X is more objective while 何Xか is subjective?
So for example if I had a big party and 343 people came I could say:
大きなパーティーに数百人が来ました。
“Several hundred people came to the big party.”
Because I know the exact number but I only want to emphasize the large number of people who came.
Whereas a guest would say:
大きなパーティーに何百人かが来ました。
“Hundreds of people came to the party”
Because they only have an idea of how many people were there.
@Kuromaku It’s been a couple months but, I asked some more native Japanese people about this and they all said that they consider them the same. They also said both were common but one man said that he preferred using 何〜か when speaking.