Su, I have looked in my stash- 331nothing, and an old color card I have #331 DMC nothing.
I am thinking that there may be a typo on your pattern and that maybe there is a correction that goes with the pattern. I have found that once and found the correction online.
The other choice is going to DMC and asking them https://www.dmc.com/us/p-us-contact.html
I hope you find your answer.
If you post the name of your pattern, someone may have a newer version and the numbers could be compared or updated that way. I hope that makes sense.
Gail

Su, I looked in my stash, in where I have all the colors, and my bag of really old floss and could not find it. If you find out it really exists because it drives me crazy not to have all the colors would you post it? I am so OCD it isn't even funny. Good luck. Pam

I agree with xstitcher and contact them. It does sound like a number ‘typo’. I haven’t found any number like that either.
I found a DMC.com phone number: (800) 275-4117 but they are only open 9 a.m. - 5 pm Monday-Thursday
And 9 a.m. -2:30 pm on Friday.
If your pattern State a NAME for the thread color ie. Very light melon, etc. besides the number, I suggest you give them the name as well for them to try a match-up.
Please Let us know what the results are...:)

Does it describe the color of 331? I'm wondering if it's 3371.....a dark brown/black

I have an older set of the DMC printed labels for the bobbins and the numbers are 327 then 333 with nothing in between. The mystery continues ...

I found a "vintage" DMC shoppers list, copyrighted 1994, and there is NO 331 listed on that either. IF it was a kit, they may have a special color made for them but those numbers don't usually fit within their "normal" numbers from the one's I have seen. If the designer/publisher has a web-site, I would check it for error/corrections.

OK...I have had done most of the suggested things to remedy. First it is a design by Tanya Brockmeyer for The Scarlett House. I have written her before, so I will ask her and wait for her reply. The pattern says it would be Espresso in Belle Soie Silks or Picnic Basket in Weeks Dye Works. I have a lot of Weeks, so I m eanng toward the typo and it being 3371. We know that 3371 is such a dark brown that it is sometime used by designers instead of 310 Black I am still going to write to Tanya and check the company website to see if it is listed there! More later...

Keep us posted. You know if there is a 331, we all have to have 2 - you know we have to have 2 of everything---just in case!

Su - Tell DH that your stitching obsession is cheaper than therapy!

DH thinks I am "mentally ill". I am sure that will remain in my "don't get mad, get even" brain for a very long time. If I tell him this hobby is cheaper than therapy, he will just argue. He refuses to go to marriage counseling. He says, "Why bother? They always side with you." That is true.
As for 331, I am going to use 838 because 3371 is far too dark for my taste. We shall see. Thanks for all the creative ideas about this. I did find an old DMC list that also has no 331. That was in 1982. Since they have been in business for a very long time, like meny years before the American Revolution and the French Revolution, I won't worry too much.