Now we have the situation where you keep restating your wish and I keep saying that I already gave you the solution. How could this happen? Well, it would not have happened if you would make your question clear. I asked some questions in return initially and then rushed to a solution without awaiting your reply - which you didn't give.
Now you state that you want two lists that you don't need in order to make a third list. I think, the formula I worked out prepares the third list. Why don't you show me at least one of two things:-
Either a list - in an Excel sheet (xls format, please) that looks like the list you want AND has the reference points in it, namely the starting date and monthly dates.
Or, a list prepared with my formula with comments added by you showing where it goes wrong. You can use the sheet I posted. Just write the results you want next to those the list provides.
I think it would be possible to construct something based on your most recent description. But, forgive me, I feel reluctant to construct two lists you don't need while I believe that I already provided the final answer.
It now occurs to me that you might actually need the two lists you want to hide. The last time I acted on such a late impuls I did a lot of work you claim to be useless. So, this time I'll wait for your response. Of course, if you do need the two lists, they should have a particular format that you should clarify. The values would have to be separated by commas or semicolons or spaces, perhaps. But most importantly, such a list, in a single cell, can't be anything but a string. So, to extract a value from the list you would have to first extract the element and then convert it to a number. That would be quite some formula - more likely code. Do you already have that?
Have a great day!
I do this for "honour and country" - much less of the latter, actually.
If I helped you, award points, plenty of them.
If I bored you, deduct points for being too long-winded. (I know, :lol)