Why didn't Kyle Reese know what the Terminator looked like in the original movie?

I thought of this question after reading another one.

Kyle Reese explains to Sarah Connor why he couldn't just shoot the terminator before it tried to kill her in the original movie.

REESE: Pay attention. The 600 series had rubber skin. We spotted them easy. But these are new. They look human. Sweat, bad breath, everything. Very hard to spot. I had to wait 'til he moved on you before I could zero him.

He was in the dance club watching her and looking around for the terminator. Reese should have recognized the terminator before it made a move.

Wouldn't he know what Arnie style terminators look like?

Skynet made hundreds of them. Reese even admitted in the original movie that the new ones looked human and had bad breath. He would either know that from personal experience, because somebody told him, or whatever. He might even have had a photo of one since the resistance would probably take pictures of it and send the pictures to other resistance cells with a note, "New terminator model from Skynet. Shoot on sight."

Answer

Wouldn't he know what Arnie style terminators look like?

Not necessarily. The T-800 is an infiltration unit. As has been mentioned in the comments above, it wouldn't make a lot of sense to make all infiltration units look like a single individual, because the first one that's found out would blow cover for all of them and render the model's purpose obsolete.

Skynet made hundreds of them. Reese even admitted in the original movie that the new ones looked human and had bad breath. He would either know that from personal experience, because somebody told him, or whatever.

All of this is true and sound logic, however, none of it establishes a reason to think that all T-800 Terminators look like Arnie. They can "look human" and "sweat" and "have bad breath" without necessarily having the same face.

Consider this:

Of all the T-800 model Terminators we see in the first three movies (I haven't bothered watching anything beyond T3 myself), only the first one was actually sent by Skynet. The T-800s seen in T2 and T3 were both reprogrammed by the resistance and sent back to help John Connor. It's entirely possible that the Resistance chose the Arnie-faced version of a T-800 on purpose to make it familiar to John in the past.

Even if Kyle Reese had seen an Arnie-faced T-800 in the future before the events of the first movie, there's no indication that he knew in advance which specific face Skynet had chosen to use on the T-800 they sent back to kill Sarah. (Actually, the very quote you bring up suggests that he did not.)

He might've known dozens of different possible faces, but he wouldn't know which one he was looking for in the past. Far more efficient to stake out Sarah Connor and wait for the Terminator to make a move, than to try and scour 1980s Los Angeles for any of a few dozen known T-800 faces.