.... The situation is :

I am installing a new knotty pine wood flooring over joist.

The pine flooring is 5" wide by 1-1/2" thick T&G by 16 lineal ft.

The joist are original to the building (circa early 1900's)
4" X 18" on 16" center re-installed to support a dining section of a new Sports Pub.

My question is this:

Is there any major consequence to screwing these boards to the joist ?
I was asked to use 4" exterior screws on the tongues which are pre drilled .

The floors look great so far.....

My concern is with the expansion and contraction of this floor and wondering if there are any major issues the builder has overlooked.?

I live in a house which was described by the appraiser as an Appalachian mountain home. It was built with 2x6 v-groove pine for the ceilings. (The ceiling is the floor for the upstairs.) It is a post and beam construction 4' oc. The 2x6's are nailed into the beams, not screwed, and due to the manner that my house was built (both length of span between beams and manner of heating and cooling), I have cracks between some boards that can range up to 1/8".
That being said, pine has a great tendency to expand and contract regardless of fastener used.
I think that screws will be fine to use on the tongue. If the wood wants to move, it will move dimensionally at the groove area, and you won't necessarily have the squeaks that typically develop with smooth nails.

Screws would by my choice, easiest and the best grip. The wood is going to move. In today's advanced construction procedures, the opportunity to take precautions now to eliminate unwanted squeaks is possible.
If this is something that interest You, I would recommend a urethane adhesive. These adhesives stay flexible, allowing the wood to move without breaking the adhesives bond. I use Seka, in small caulking tubes.
Best of luck, Dan