We know serial numbers weren't produced and used in numerical order.
Groups of numbers may have, like some bags from around 1992 that still used the old 3+4 format and started with 0xx-xxx. But lower sequence numbers DON'T mean older bags.
My guess is that the early Twill bags like the ones in the above listings would have been from around 1986, which is the earliest mention of a line of twill versions I can find. The 1986 Summer catalog says " Some of our most popular styles are
now available in Khaki cotton twill..." (italics mine) which seems to say that the twill is a recent addition. So if those and the one in the picture below which may be from a #8635 Convertible Clutch in Twill have serials starting with 988- or the 967- in Sacsmag's Slim Satchel Large Twill, those numbers certainly weren't used in a straight sequence 000-0001 to 999-xxxx.
I agree that the Slim Satchel was probably a very early twill bag (it's shown in that 1986 Summer catalog below along with the Twill Convertible Clutch), and
Coach might not have had the Twill version creed stamp ready for production yet so a standard one was used. Or the plant just made a mistake.