On the other hand, there's no specification regarding multiple attacks which don't derive from a high base attack bonus. Off-hand attacks, Rapid Shot, Flurry of Blows, Haste, and so forth are all ways to gain multiple attacks which come from sources other than a high base attack bonus... so in theory, your three off-hand attacks from GTWF could be made at +1 then +6 then +11 (or whatever). (Unless one considers that 'gain a second attack' and 'gain a third attack' specify chronology... but it still allows for your highest bonus off-hand attack to occur after your lowest bonus primary attack, and Haste, Rapid Shot, Flurry etc can all appear anywhere in the sequence.)
-Hyp.