While you are correct concerning the 1999 to be the first year of the MC250, the article in Dirt Rider (I think it was February, '99.) was on the '99XC250 and the EC200, which were the first year models for both. I bought the EC200 test bike for the article the week after the test, and my youngest son, Brandon Butler, still rides that bike.
If the article says it was on the EC250, and not the XC, then bike was misrepresented in the article. That XC250 passed through my shop on it's way to a sponsored rider in Texas.

The numbers at the first of your vin # will tell you more than the numbers at the end, and yet they may not tell you what you want to know.
The numbers at the end of the frame vin number are "run numbers". Since the number ends in I would guess that your frame may be the first of it's run, since it ends in 001. What is your whole vin number on the frame?
Is your transmission a 4-speed?

Jim,
Thanks for the information. The VIN is *VTREC259811975001* on the head stock and again on a frame tag on the leading edge of the frame aft the front fender. There is a code on the botom of the engine on the kickstand side which is MC25-98 above
S 11975000 and it is a 4 speed. I was told the engine was sent back to Gas Gas for repair after a race and then placed back in the bike. Any additional information you can provide would be much appreciated. I will work on acquiring the Dirt Rider issue as well.

Legacy

I'm curious about the frame.
Does the steering head of the frame have the steering lock on the side of it? The early model ECs had the lock, and your frame serial number identifies it as the frame for a 1999 EC250 (VTR"EC" = EC, "25" = 250, and the "9' in 259 denotes the year 1999).
Other than the having 50mm Marrazocci conventional forks instead of the 45mm, there was no difference in the chassis of the MC and EC, beside the loss of the steering head lock. (grasping for memories, here, but my son, Gabriel, says that his '99 MC250 4-speed had no steering lock.)
My son, Joshua, still rides his '99 6-speed MC250. (It was specially built for a sponsored MX rider by GasGas North America, my first US Importer of the enduro bikes.)

I have that issue, it's the Dirt Rider test of the EC200, XC250 fown in Mississippi.... I burned a copy of it and posted it some place....