This is going to be a column about a little "T and A." And before my readers start blushing because of the naughty images that phrase might conjure up, I must confess that it's not what you think. This is a boring old Social Security column, after all.

A couple weeks ago, I wrote a column about something called "beneficiary identification codes," or BICs. These are little letter symbols that follow your Social Security number once you apply for Social Security benefits. They designate the kind of Social Security benefit you are claiming. Your "claim number" (a Social Security number with a little BIC symbol behind it) will show up on any official correspondence you might get from the Social Security Administration. And it's most often noticed by people on their Medicare card.

For example, if you are getting Social Security retirement benefits, your claim number is your SSN with the BIC code "A" behind it. That "A" stands for retirement benefits in Social Security records. And if you are over 65 and on Medicare, your Medicare number is your SSN with the same "A" behind it.

Because many people claim benefits from a spouse's Social Security record, their claim number (and corresponding Medicare number) will be the spouse's SSN with a different BIC symbol. For example, if you are a woman getting widow's benefits from Social Security and your deceased husband's SSN was 987-65-4321, your claim number and Medicare number would be 987-65-4321D. The letter "D" stands for widow's benefits in Social Security records.

Many women are getting a combination of their own retirement benefit and some extra money from their husband's Social Security account. Almost always in those cases, your own Social Security number is the primary number. So your claim number will be your own SSN with an "A" behind it.

These BIC codes generally run from "A" all the way to "W" and designate the many different kinds of Social Security benefits available.

One of those codes is a "T." And in the prior column, I wrote that "T" means you are insured for Medicare benefits, but you are not insured for Social Security benefits. And that was wrong! (By the way, "insured" means you have at least the minimum 40 credits, or "quarters of coverage," to be eligible for benefits.) I didn't think too much about this BIC code and my definition of it because "back in the day," i.e., when I worked for the Social Security Administration, there weren't all that many "T" beneficiaries. Most people worked and paid into Social Security and Medicare at the same time, so they were generally insured for both programs. Even those folks who spent the bulk of their careers working at jobs not covered by Social Security (but that were covered by Medicare) spent enough time working at other jobs where they did pay into Social Security so they were "insured" for both programs, meaning at retirement they were "A" (retirement) beneficiaries and not "T" (Medicare only) beneficiaries.

Unfortunately, judging from the ton of email I received, my incorrect definition of a "T" beneficiary confused more than a few readers who are "T" beneficiaries but who are indeed also insured (or eligible for) Social Security.

In the past, during most of my 32-year career with SSA, a person had to file for Social Security benefits at age 65 in order to get their Medicare benefits. Even if they were still working or otherwise wanted to delay their benefits until a later date, they still filed for Social Security at 65 to get Medicare coverage. Then their Social Security benefits were immediately suspended until whatever later date they wanted to claim them. But the point is, they had filed for Social Security, so their BIC code was "A" because they were entitled to (although not yet receiving) retirement benefits.

So the "T" code was reserved only for those very few people who were not eligible for any kind of Social Security benefit but had paid taxes into the Medicare program.

But when the full retirement age climbed to age 66 and people affected by that change started reaching that age, SSA had to change their claims filing rules. The rules now say that you can file for Medicare at age 65 without having to file for Social Security benefits. And these folks had to be given a claim number. It couldn't be an "A" BIC code, which again means you are getting retirement benefits. It had to be the "T" code, and the definition was changed to: "entitled to Medicare but not yet entitled to Social Security."

That is very different from the old and incorrect definition I gave in the prior column that said "T" meant you were "insured for Medicare but not insured for Social Security."

There are currently millions of "T" beneficiaries, and I confused that small share of them who read this column. If you are a "T" beneficiary (meaning your Medicare card shows your SSN with a "T" behind it), you are very likely to be a person who took Medicare at age 65 and you are waiting until age 66, or possibly even age 70, to apply for Social Security benefits. Whenever you do that, your claim number will change from your SSN with a "T" to your SSN with an "A."

And that's about the most boring discussion of "T and A" that you will ever read!