Knotty Pine room

If it is shellac, you are in luck. The nice thing about shellac is that it can be used as a barrier coat and a seal coat for most anything. Seal knots in wood, for instance. Try an inconspicuous spot and it will probably work.

Strip the oil finish that is what is dark not the wood, alcohol removes shellac, paint remover varnish. People pay alot for natural wood , it may come out near new looking for little work. Water base varnish to reseal it will not darken like shellac.

">I have a family room over my garage that was finished with interlocking

Won't be long before knotty pine will come back in style like gang busters. Don't be too quick to paint it. A good cleaning/sanding/reshellacing may make it much brighter. If you must paint it, shellac can be a stain blocker, but if it is old, the knots may still bleed their pitch thru to the surface of the new paint. To seal it for sure, use zinsser or other such stainblocker, then paint with opaque paint, but this approach will obscure all traces of the knots , which you apparently don't want.There also may be a way to bleach the surface with chorox, before refinishing - we have done this before, with good lightening effect. You might also get opinion of expert painter that deals in faux finishes and various washes.