Now into the sixth month of the big kitchen overhaul and there is light
at the end of the tunnel (probably a torch I bricked up in the wall).
Have completed steelwork, slapping, brickwork, leckie, plumbing and
plastering. Next job is the floor.

The kitchen floor is mostly original 100 year old imperial floor boards
with one smallish area redone in newer 136mm boards. It has been sanded
and varnished thought this needs redone now.

As the kitchen is now bigger, there's a whole new area to one side that
will require flooring with new boards, hopefully macthing.

Overt the years the existing floor has been hacked about a bit for
access and in most of these holes the removed sections damaged by the
initial and repeated removal. I'm not sure about sourcing matching
boards to repair these holes so intend to lift a whole board (or two)
from the edge, next to the new bit anyway, and use those to make
replacement parts for the holes.

So, the questions:

Where sections of boards have been lifted noggins have been nailed to
the joist to all.In some placed the noggins have sagged a bit. I
thought I could use a router to cut back the existing (fixed) board
halfway over the joist so as the replacement board sits on the joits at
each end. Worth the effort - I'll be cutting new sections to fill
anyway so the change of length ois no an issue?

Secondly, how to fit them in. The obvious way seems to be to cut the
bottom lip of the groove (and maybe sand the tongue a wee bitty) so
that they'll slot in. Any other/better suggestions.

There may be one long joint where I have to tongue/groove old and new
boards together. I can get the right thikness, but if the
tongue/grooves don't match what's the best way to acheive a good join.

Should I treat new boards with anything before fitting. The underfloor
area is (thankfully) dry as a bone?

Any hints on making the new boards match the old boards?

Soryy for the long post, thanks for all your help.