There are 2 styles of rollmarks on the originals––large and small.
The current production Series 70 pistols have the small style roll marks only.
Current slides say "Colt Government Model", most of the originals say "Colt's Government Model" with an apostrophe s.
All current production Series 70 serial numbers start with "71B", many original Series 70s start with "70G" though there are other prefixes also.
Stainless pistols have only been made in the current production, there are many nickel and chrome early run Series 70.
Quality on the original guns is hit and miss, there are some real dogs out there with slide lug issues and off center frame dustcover machining that are very expensive and difficult, or impossible to fix. Current production pistols are consistently very high quality and well made, though you do have to watch for the "off center" slide bore/recoil tunnel/dustcover" issue.
I would not pay a premium for an early Series 70, the current Colts are some of the best pistols they have ever mad–– make sure it has all original Colt parts especially the barrel, that no one has messed with it––especially the feedramps.