We lost part of our calendar. We are missing a month many months ago from what we were able to recover. Do we just continue going? Do we put in onah beinonis for that month?
If the date that was lost wasn’t a very recent month, but only a few months back, there isn’t much that you can do about it. (It is possible that a period after that erased it, and even if that period was longer, it might have had a number of smaller spaces after it and we won’t be concerned about it.)
Regarding the Onah Benonis, and Yom Hachodesh which is days 30 (and according to some poskim day 31), and the that goes according to the last period that she had, therefore her missing dates will not affect the Onah Benonis.