I honestly don't believe they were Q all along. I think they were Q starting from around when Q moved to 8chan or maybe slightly later, but I don't believe they were the original Q.
EDIT: Want to be more specific. So, 4chan/8chan have this thing called tripcodes, where you supply a password and it salts and hashes it and shows the result by your post. The idea is that since you don't have an account per se and can change the name you post as at will, it acts as a form of attestation that the user behind two or more posts are probably the same user.
If you look at the pattern of Q posts for each tripcode, you see a pattern that looks like what you'd expect if about a half dozen people were Q semi-interchangeably (different ones more dominant at different times, but never a single tripcode long term and never exclusively or near-exclusively one code for more than a month or two) until September 2018, after which virtually all Q posts come from one tripcode for several months then virtually all Q posts come from one other tripcode afterwards, with the tripcode switching at the same time 8chan changed their salt (which necessarily changes the result of the hash).
My personal belief is that once we switch to essentially one tripcode behind Q, that's when Watkins became Q. Before that it was probably several conspiracy trolls building on a shared mythology with each having partly overlapping periods of high activity and then mostly wandering off to do other things.