Doing auto-numbered paragraphs in Word mailmerge is, as you have discovered,
a pain.

One possibility is to use { SEQ } fields to do the numbering. However, {
SEQ } fields do not behave well inside IF fields.

As long as the number of possible combinations is small it may be simpler to
a. identify the "paragraph schemes" you need e.g. one with paras 1,2,3,4,
one with paras 1,2,3,4,7,8 or whatever
b. do not use autonumbering
c. put the complete text for each "paragraph scheme" in a different branch
of an IF field's results.

Nasty duplication but it's much more likely to work properly.