For flooring an extension to my Victorian house I am planning to use
reclaimed victorian floorboard (with suitable insulation under). ebay
item 220474833588 is an example.

However, an alternative is "resawn floorboards" where the supplier has
sawn up victorian joists to make 'new' old floorboards. ebay item
130325590872 is an example.

Is there anything to aware of with such resawn boards? is the joist
wood likely to be softer for example, or to have more knots in it?

Robert