Underfloor Ventilation

What's the stitch with underfloor vents... I'm still looking at the sub-floor thingymebob of the front room at our place. It has vents along the side wall... and that's it as far as Ican tell. I think this room was a later addition to the house many many years ago and that side wall may have originally been the fron of the house as there is what may have been the front door on that side of the house (in the next room). The now front of house has a slab of concrete(porch/veranda) so putting vents in mightn't be possible. But there is still only vents on one wall .... Is this ok?
making sense?

The other thing is the next room over ...after the hallway- has been 'sunken' and is lower than the vents which are on the oppsite side of the house..... this room is on the side of the front room which has no vents... maybe the reason there is no vents?

If this is confusing.... got any advice on vents...?

Well, the advice is you need em! At least if you have any damp down there.

You need cross flow.

I had a similar prob to yours with an extension so where I couldn't add vents I put in a couple of wind-powered exhausts. Fancy name for a 90mm stormwater pipe with inlet under the house and run up to a 6" rotary ventilator above the roof ridge line. One ran outside the house and the other I routed through the linen press and up through the roof. The inlet is sited as far away from the vents as poss. to encourage air flow.

Worked so well, the wood floor dried out and shrunk enough to create a quarter inch gap in the cork tiles. Least it's now dry!