And I was thinking the numbering should be offset by 1 so that it was numbered beginning with ZERO and ending with 2047 = zoo.
This is correct.
You first generate 256 bits of entropy, then use SHA256 to calculate and append the 8 bit checksum. You then split the resulting 264 bits in to 24 chunks of 11 bits each. These can range as follows:
00000000000
00000000001
00000000010
00000000011
00000000100
00000000101
00000000110
00000000111
00000001000
.....
11111111111
00000000000 converted to decimal is 0.
11111111111 converted to decimal is 2047.
I'm surprised the word list got published like it did... but I guess their thinking was, it was a list of 2048 words and they numbered them accordingly.
The wordlist (
https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt) was published as a list of words without associated numbers. It is only numbered because GitHub uses line numbering starting from 1.