The second column states the number of days difference between 365.24... day calendar and the 364 day calendar, and for the mathematically challenged among us (me) the 3rd column states the same thing as the number of mean solar months (30.333333 days). So, anything close to 2.00 is "two" of said average 364 day year months. In actuality the months were ordered as two 30 day months followed by one 31 day month, or alternatively, they were all 30 day months with four single day adjustments every 3 months. This is kind of like the Egyptian year, which was 12 30 day months, but with five adjustment days at the end of the year.
I see what you're getting at now. There is a deficit of 59 - 60 days over any jubilee period, so two months would have to be added to a 364-day calendar. Presumably, one would be added after 24 years, and the other after 49? It would work as a solar calendar, I think, but I can't see it fitting with 'New Moons' etc. Also, the Qumran community were fanatical Sabbatarians. I doubt that they would have been happy about making an adjustment on the 24th year. (21st year maybe. Either that or they waited 49 years before adding 2 months.)
What I am thinking they did was add an extra week every few years to get things on track, maybe tacking it at the end of a year as a special festival week. It has been some while since I have read anything about it (although I have a bunch of books and articles that touch on the subject of DSS calendars) but I seem to recall that the calendric writings refer to festivals that are not otherwise known from the Luni-Solar calendar of Babylon or modern Judaism. They were fanatical about having each specific festival day fall on the same day of the week each year.
The thing is, despite their fascination with multiples of seven, their basic month is 30 days, which is not a multiple of seven. To add 30 days (or 31 days) will not yield a multiple of 30 and the day of the week of the festival would shift, which is a no-no. So I suppose they could have some other scheme to intercalate. Thirty is a multiple of 5 or 6 (6 x 5 = 30). To harmonize, the solution would have to be some factorial of 5 x 7 = 35 or 6 x 7 = 42. Thirty five days variance happens between the 28th or 29th year and forty two days happens in the 34th year, so that means either 5 weeks in 28.5 years or six weeks in forty two years. The former is hard to get a smooth result from but adding a week every 6 years might work.
Basically, an extra week is added every 6 years, and another week was added two years after the 8th intercalation (year 48), that is, the 50th year. The start of the next intercalation 50 year intercalation scheme (apparently not same as the system for measuring years of time) varies from a true solar by just -0.370050 day at the start of the next cycle (the 51st year). Then an extra week would only need be added every 19 of those fifty-year cycles (i.e., every 950 years). That's a lot of time before you would have to introduce a secondary intercalation! You can't wave a sheaf on the designated date if that falls in mid winter. The dates of festivals, etc., need to keep in track with the seasons. This intercalation system is never more than one week off. That is pretty damn close.
On the other hand, the years-of-time counting scheme seems to have been based on multiples of 49 years, not 50, but those years still need to be intercalated, so the two systems, one for counting time and the other to intercalate with the seasonal years, must have been maintained at the same time. Then years of this entirely calculated time tracking scheme can be synchronized with other calculated cycles, like the luni-solar Babylonian and the Syro-Macedonian calendars, or the priestly rotation for service in the temple. The common denominator for synchronizations like this is that they are calculated schemes. On the other hand, annalists (recorders of events) probably used synchronizations like these to correlate events in history with fixed cycles. "This or that priestly family was in service in the temple when king so-and-so attacked a certain town or city," etc.
I'd love to claim credit for this idea, but I believe I have read it proposed before.