It is still possible to count accurately from the post history, any post that has been moved or deleted could be easily spotted as well and you can just count backwards to the timestamp. Every post is even label with their respective board. Also, ninjastic.spcae & the beta version are available for that too
Counting backwards to the timestamps of the deleted post can very stressful and frustrating
, I am already imagining how tedious this kind of self inflicted task can be especially if the post happens to be a very old post or such that it's timestamp and index are far from the current post. ninjastic.space as suggested makes it more easier and saves time