Dwight, you are correct, the bottom edge of the side plate does have a number #45, a mismatch. The center toggle has no proof but the bolt and the rear toggle do have the c/V stamp. I'll get a pic of the witness mark for you . I think Ron might have the answer, the 1933 date may have been a rework date for something else, the side plate maybe? as the barrel does still have it's original stampings even though it definitely has a different appearance and finish from the rest of the slide assembly.
http://forum.lugerforum.com/lfupload/witness_mark.jpg
Just barely visible in this photo is the unusual location of serial # on the thumb safety lever, on the inside rather than on the edge.
Ok, I'm completely confused now. Having taken the time to do a little more research in Martens and de Vries I find the following: "Finally, a completely different set of proof marks is (sic) found on the Dutch Vickers Lugers. These pistols were proofed in England, and marked accordingly. At the underside of the barrel, they were struck with the letters "NP" (nitro-proof), the crowned, entwined letters "GP" (the definitive proof mark of the London proof house) and a crowned "V" was also struck on the most of the pistols' principal parts, such as the toggle assembly, breech block and frame.
Underneath a photo on page 163 showing a barrel date of 1925 the caption reads "Most Dutch East Indies Lugers have a small date struck at the top of the barrel. As pistol barrels wore out quickly in the tropical climate, they were replaced every six or seven years. The date signified the year in which the barrel entered service. The earliest year observed is 1914, the latest 1941.
Since this Vickers has the original proof marks on the barrel as well as the date of 1933 on the top of the barrel it must indicate something other than a routine barrel replacement unless there happened to be a quantity of spare barrels that were originally proofed in England, and then serial numbered to the weapon following replacement. The barrels that were made in the Indies were stamped with the arsenel stamp, GS, however there is no mention of there being a supply of original Vickers barrels used for replacements.