Month_No between 1 and Parent?

[RahelWalther]

I have a subreport where I have a running sum calculated for ascending months of a year. I wanted to link a main report to this subreport. The main report displays only numbers per month. If I link the two date fields in main and subreport, the subreport does not display the running sum from January to the date of the main report, e.g. July, but displays only numbers for July.
Then, I tried to create a new field in the main report that displays the number of the month of the main report, e.g. 6 for July. In the subreport, I created a new field Month_No2 that has the following syntax:

Field Month_No2: Month([SignedDate])
Total Expression
Criteria Between Month(DateSerial(Year(Date()),1,1)) And [Parent]![Month_No]

I also linked Main and subreport through Month_No2 and Month_No

If I open the report with this subreport, the subreport does not show up, so what I did must be faulty, but it seems that something like this should theoretically be working out.
What I want to do is to display numbers in the subreport between the first month of the respective year (1) to the month of the main report (e.g. 6). How, if at all, can I do that?

Any help is greatly appreciated.

Greetings, Rahel