[size=12]Personally, I don't cook with my collectable iron, but there shouldn't be any difference using a piece that calls itself a "baster" compared to using an otherwise-identical-down-to-the-pattern-number piece that calls itself a "dutch oven." I don't know why Griswold changed the wording, but just like Perry said, that's absolutely all that they changed. (Well, eventually they started putting easy-clean black coating on the undersides of the lid, and they stopped casting tabs into the lid, but that didn't happen until after they had already made the change in nomenclature. And older Basters with the slant logo had a much flatter lid rather than a domed lid.)
Later pieces mostly said "Erie, PA, U.S.A" instead of just "ERIE." I think that change happened sometime in the early- to mid-twenties. And there are variants that have a different arrangement of the printing and the patent date, but I think most of those are older slant-logo EPU ovens. Your combo is mismatched, but it may have come that way from the factory. Consensus has it that if they had a bunch of one type of lid to use up soon after having made the baster/DO change, they just cast new-name DO bottoms and sold them with old-name baster lids, or vice versa. Since there was no functional difference, nobody cared until much later when maniacs like us started collecting this stuff. I'd guess that your piece could be from the mid-thirties to the late forties, but I can't peg it any more specifically than that. The 5th ed. blue book (The Book of Griswold and Wagner by Smith and Wafford; get one if you want to start collecting Griswold) says 1920-1950, actually.
2603 was the pattern number for the size 7 Dutch Oven (or Baster) bottom. That's just the manufacturer's number for sake of keeping track of that exact piece (or more accurately, the pattern used to cast it) in the foundry or the warehouse, in whatever iteration it was currently being cast in. The lid should have a 2604 on the bottom side of it. March 16, 1920 was just the date that the patent application for the locking bail was granted. If you want to look up more information, go to the US patent office's website and research patent no. 1,333,917. As far as having the company name on the top and the description of the piece below that... that's perfectly normal for Griswold's Dutch Ovens. This isn't any odd variant. They did the opposite for the skillets and griddles -- "Cast Iron Skillet" or what-have-you was on top and the company info was near the bottom, on the other side of the logo. I couldn't tell you why they did it that way, or even if they thought twice about it, as long as they were getting saleable and useable hollowware on the market. Several collectors have said that the only thing consistent about Griswold was its inconsistency.
A size 7 is a little more rare than a size 9, and a size 8 is rather common. The pitting hurts the value, and that's doubly true if the inside is also rough.
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