Sorry, but I am with Montemeyer on this one (and I am still intend to telephone you Art-forgive the personal note).
The reason that seal welding is done first is to allow the welding gases behind the weld to escape along the tube. To roll first means that the gas is trapped behind the weld at the point of closure and it will blow out at the end of the pass destroying the seal.
The only exception is titanium tubes to titanium tube sheets where the proper procedure is to roll first and then weld.
If a seal welded joint is properly expanded, whether by rolling or explosive or hydraulic expansion, the expansion needs to begin about 1/2" behind the seal weld so that there is no danger of mechanical damage to the seal weld. Anyone who would roll or otherwise expand too close to the seal weld doesn't know what they are doing. Some explosive expansion charges have a duplex charge where the leader is a lower charge cardite and the cardite that does the expansion is a higher charge weight. Others don't-the cardite is uniform from the leader to inside the tube. Watch those guys.
All that said, a high pressure Feedwater heater (5000 PSI working pressure) on a supercritical unit in a state up north of where I am now was found some years ago to have a row of tubes where the entire row had failed to be expanded and it wasn't detected at initial manufacture. The error wasn't caught until the heater was field re-tubed some 15-20 years after it went into service. So much for seal welds not being strength welds. But, then again, the exception doesn't make the rule.
Unclesyd and I had this discussion some years ago in this same forum I think, and he has a different take in that he had a lot of success with the reverse of the process I advocate, so how can you argue with success.
A search can produce that discussion.
Most of my experience is in high pressure stuff, so I can't address low pressure heat exchangers.
rmw