peck & snyder
 

Can someone tell me why PSA only grades these as authentic?

It may be that they are not sure what size they were at the time of issue. So many have been trimmed that they may fear all have been altered to some degree. Also, the red ones are smaller than the black ones, creating even more confusion. They may feel it's better to be cautious than to risk a big problem down the road.

I know SGC has given a numerical grade to some, but they too may find one that they can't be sure is original.

thanks
 

thanks Barry that is what I thought but the fact that SGC grades them seemed inconsistent

Any experienced 19th century collector will have no trouble detecting trimming in P & Ss. Therefore, there is no reason such cards cannot receive numerical grades. Same applies to cabinet cards and Cdvs.

experience
 

I don't think they have enough experience with them either (or vintage in general, actually), in order to do them a good service. As Corey said, anyone with knowledge shouldn't have a problem grading them. Since cards usually go for more in a numerical holder, all things being equal, than an AUT holder, it's hard to believe folks would send them their Peck and Snyders. best regards