Colt Officers Model 38 Serial Numbers

Hello all
Like some of you, I have just purchased a Colt Officers Model (38) with a three day inspection period and am struggling to confirm the year of manufacturer. It is supposed to be a pre-war model. But I would like to confirm this as part of my inspection period. From reading many forums, I am appreciating that dating these old revolvers is a bit of an art. So your help is appreciated.
Here is what I know.
The serial is 603-xxx.
It has a checkered cylinder release, checkered back strap and checkered trigger.
The barrel has stamped 'OFFICERS MODEL .38 HEAVY BARREL' and 'PATD AUG 5 1884, JULY 4 1905, OCT 5 1928'.
The front sight is adjustable for elevation (Patrdige?); the rear sight is simply adjustable for windage.
From a similar question to which Dfariswheel replied back in January 2011, I am pretty sure it was made sometime around 1935 and is a model Target.
I did find an old magazine ad from 1940 that described the heavy barrel, but that ad included 'Target' on the barrel which mine does not.
Any suggestions or advice.
Many thanks.

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It was a medium frame Colt.38 Special having the patina of steady use over a long time. It was an Officer’s Model.38 whose serial number put it leaving the Colt factory just over a hundred years ago.