Lambing Period for Recently Acquired Ewes

I contacted the previous owner of our recently acquired ewes to ascertain the precise dates the ewes had rams with them leading to current pregnancy. From this we can then determine an accurate total lambing period, for planning purposes.
Here are the dates and forecast dates:
"Teasers" were introduced to the ewes on 2nd March 2009 and were removed on 16th March. The theory of having 'teasers' with the ewes is that it is supposed to heighten readiness for service.
Rams were introduced on 16th March 2009 and were removed on 20th April. Thus, based on the standard 150 day gestation period for sheep, we can expect the ewes to lamb from 12th August through to 16th September 2009, although there will be some variations outside these dates.