rare? or rebarreled? all steel colt "agent"

Hi,
I have an all steel colt, with a rather unusual feature. The barrel is marked "Agent". To my knowledge Colt agents came as alloy frame guns only.
This one has the high polish blue finish, pachmayr grips with no logo, and a shrouded barrel.
The serial number is an S prefix. That makes it a detective special frame, sporting an agent barrel. OR... perhaps it was a frankenstein gun put together from leftover parts at the factory, and left the factory as one of the only "steel" colt agents.
I have seen a few other supposedly "all steel" colt agents for sale.

http://www.gunsamerica.com/960831422/Colt+Agent+38Sp+2+rare+steel+frame.htm

that's another one I've found. It looks really fishy though.

I guess what I'm looking for is a reason to either pay for a letter from colt,
or just call it someones rebarreled shooter.

A reason to call it a shooter would be if someone can remember a run of new old stock agent barrels being available..this one has a sort of different bluing between the frame and barrel, like it wasn't blued at the same time or with the same methods or..didn't came on the gun,
although the cylinder is the same color bluing...
The frame is definitely steel though. If it were rebarreled though, it would be a pretty good rebarrel job to my admittedly untrained eye. No tooling marks or shiny threads, no bluing marks at all. The rollmarks are all crisp, to me.

A reason to send in for a letter is if it could have value as something of a rarity as one of the only colt agents to leave the factory with a steel frame.
I'm perfectly happy for someone to burst my bubble so I can enjoy shooting the heck out of this thing :)

Thanks

http://pictures.gunauction.com/876/11256285/colt%20agent%20right.jpg_thumbnail0.jpg
http://pictures.gunauction.com/876/11256285/colt%20agent%20left.jpg_thumbnail0.jpg

We can only speculate.
Factory error?
Parts cleanup?
Conversion of a Police Positive Special to snubby?

It will cost you $75 to get an idea of what was going on.
Will that information increase the value of the gun by more than $75?
Certainly not if it is a replacement barrel, maybe if it is one of a known small number of parts cleanup guns. Error guns don't seem to draw premium prices.

I have an Ace .22 with a 70B serial number as for a .45. I have also seen the reverse, a .45 with SM serial. Colt is not real careful about such stuff.

If I have a DS with a bad barrel and write GPC and they only have barrels marked "Agent", what do I do? Maybe I make a gun that will cause folks on the Internet 30 years in the future to ask about the rare gun.

Jim