Yesterday's column ended with an unanswered question: Did the United States Postal Service short-change a customer who thought he was buying a roll of 100 15-cents stamps?

The newsletter published by the National Press Club's American Legion post is mailed to precisely 125 members in precisely 125 envelopes. Post commander Charles McAleer went to the Ben Franklin post office and asked for 125 stamps. He was given a roll marked "100" plus 25 stamps torn from a large sheet.

However when the stamps were all affixed, nine envelopes remained unstamped. The question, therefore, was: Did the Postal Service sell McAleer a 91-stamp roll for $15?

Madam Spokesperson, the woman who usually looks into postal complaints from readers of this column, was taking a day of annual leave when I called. One of her male colleagues stepped into the breach and launched an immediate investigation.

He talked to postal supervisors and postmasters and quality control people, and it was agreed among the lot of them that the only way to be sure about the situation would be to begin spot-checking 100-stamp rolls all over the metrepolitan area.

Before the day was out, 107 rolls were broken open at random at 35 different postal facilities.

Each roll contained exactly 100 stamps. "During the manufacturing process," the spokesman told me, "they've counted electronically, so there is very seldom an error. If the power fails during the run, a few rolls might be affected, but even defective rolls are handled automatically. The machine shunts them aside. Last year we turned out 75 million rolls and had 15 or 29 complaints natiowide from people who said they got fewer than 100 stamps. That will give you an idea of how extremely rare it is to encounter a 100-stamp roll that doesn't contain 100 stamps. It is almost unheard of for a defective roll to get into circulation."

Well, rare stamps are valuable, and extremely rare stamps are extremely valuable, so perhaps we can auction off the nine stamps that were missing from McAleer's roll. Who'll open the bidding with $1,000 for nine stamps that are so rare you can't even see them?