Many of signature campaigns ask for the users who wish to apply the number of merits the received in the last 120 days and of course when one takes a look at one's profile (on the merit section) one can see the history of the merits we all received within this period of time. Now, would not be great if above the total history of merits there was a summation of all those merits received/sent?
I have found myself in the situation where I counted those merits manually before applying to a campaign

As you are already aware about how to have the stats for your merit information through bpip.org and you could check the other information also like total posts, deleted by moderators and your rank on the forum as well and you can also check the same for other members also on it.So now you don't need to manually count it now

You have followed yourself by thinking about something that is not worthy of attention, for example, not all campaigns ask you to participate in the number of Merits you have earned in 120 days, and who did this with the main purpose of that is making sure of your activity during the recent period and making sure that the style of writing has not changed with the acquisition of those Merits.
Yeah that's not giving more focus on according to me as well as the number 120 is random but you can say @theymos found it baseline so he might have choose this number in IQ prank also but not much of attention towards it.
For the signature campaign not all of them have these requirements for past 120 days but the reputed mangers have this criteria setup to check the users have that post quality for the selection and yes their posting style nothing else as there is no fixed criteria for the campaign manager.