Are they seriously expecting people to carry forward the number of I/F approaches they've ever flown? In the old logbook, columns 11 &12 were clearly marked to show that carry forward wasn't required.
Is there a definition of 'synthetic' time at the front of the book? Or does it really mean all box time?
Trying to establish in any detail how much box time you've ever flown would be pretty difficult, although there should be periodic summaries in Section 7 you could use for total time. I'd use those, plus an educated guess at the I/F time (80% of total?). But i'd strike through the 'carry forward' for I/F approaches.