I own a travel agency, although in Australia, where most travellers (87%) still prefer agents to other ways of booking travel.
I think this was probably a mistake, as if Trailfinders was going to give you a voucher, they may have made the reservation through a wholesaler. If this was the case, the wholesaler would definitley not send your details to the hotel until 1-2 weeks before the stay. They would just hold the reservation booked under their company's name. This is industry standard practice.
Second, SPG points/status are definitely earned if you booked through any travel agency in the world, as long as that agent makes the reservation i their CRS/GDS (global distribution system). I do this many times every day and make my own reservations this way and manage to always get my points and status. I lso have access to special rates negotiated through a multi-billion dollar buying group, which sometimes, but more rarely these days, comes up with a lower rate which is still direct through Starwood, or any other hotel chain, and therefore eligible for points/status. The only instance in which you wuld not earn SPG points when booking through an agent is when the agent uses a wholesaler.
If you just have a reservation number and you pay the hotel direct, you will earn points. If you get a prepaid voucher, you won't.
Sorry for the rant but I'm regularly annoyed when incorrect details about dealing with agents are mentioned. In Australia, the only way to be guaranteed of your services being offered is by booking through a travel agency as they are all bonded by the Travel Compensation Fund. If a company goes broke and yo lose yor money - you can claim through that body.
Sorry again for the extended blurt.