In this specific case, I’d say it’s fine to have a wide perspective on the number of historical posts, but since the thread stated on May 2014, a lot can have happened in between. For example, if historically the activity was very low, but has picked up traction over the past six months, the traction is diluted in the average over such a long period of time.
It would be better to complement it with the number of posts, month per month, over (let’s say) the last six months. Ideally, that would also have a reading of the number of distinct posters in that period (to discard heavy activity created by just a couple of forum members), although this latter aspect is a pain in the back to do it manually.
Having said that, numbers are not that great to justify a Local Board I guess:
month from to nDays Avg/day
01 2020 4404 4456 22 02,41
12 2019 4277 4403 31 04,10
11 2019 4251 4276 30 00,87
10 2019 4214 4250 31 01,19
09 2019 4163 4213 30 01,70
08 2019 4129 4162 31 01,10
Avg 6 months = 1,87 posts per day. There is a slight recent increase these past 2 months, but nothing that shines of its own light.