No, they fixed the limit when Smith's doctor regenerated, since he was
supposedly on his last life. The Time Lords gave him some more
(apparently it's not some inherent in the biology, but within the Time
Lords' gift. Odd that they don't all just live forever, then).
Tenant's return may be a last-ditch effort to undo the damage done by
Chris Chibnall (albeit with the connivance of the BBC). Would have been
better to get Capaldi back, and claim that the Giball time was just a
bad dream (do Time Lords dream?). Hey, it worked for "Dallas".
Sylvia