Bad, tragic or just trying very hard to behave, Britney Spears can still, (almost), attract a following. The BIG question on Monday night was which audience. And it’s enlightening to see precisely where this pop star in decline fits on TV ’s pitiless measure of celeb recovery.

Her small cameo role on the CBS show “How I Met Your Mother” was a big gain for the network: her attendance gave the sitcom its highest viewership of the year. But that doesn’t mean that Ms. Spears is well & truly on her way back to past glories.

It may have been sadder, because there are far lower rungs on the show biz ladder. Ms. Spears did not have to be hazed on a cable reality show like “The Surreal Life,” or arrive on the scene dazed on “Celebrity Rehab With Dr. Drew.” CBS gave her the part of a receptionist on a fairly popular network sitcom, though she was not the episode’s top-rated guest star and had to agree to take second billing to Sarah Chalke, a star of “Scrubs” on NBC.

That small, meticulously pared-down role — she played a shy & retiring receptionist in big eyeglasses who develops an unrequited crush on Ted (Josh Radnor) — was not sufficient to recharge her career or whitewash her rep, albeit she did perform acceptably. One line did test to see if it is too soon for her to joke about her unsavory image: her character asked the show’s Lothario, Barney (Neil Patrick Harris), if it might be O.K. to have sex before they go shopping. (It is too soon.)

The very fact that she managed to recite her lines was a relief: the most lasting TV image of Ms. Spears in recent times showed her tied down to a stretcher!

But the most likely comeback opportunities for the tarnished or has-been are network reality competitions like ABC’s “Dancing With the Stars.” That series (and its many lookalikes) provides full vent to the highs and lows of show business; each dance number is a balletic metaphor for disgrace, exhausting exertion and clemency. Priscilla Presley and Monica Seles are re-establishing their celeb credentials this season; last year Heather Mills, who was then pursuing a huge divorce settlement from Paul McCartney and at the pinnacle of her public distain, danced with a prosthetic leg and just about managed to win over American audiences — for a while.

Network sitcoms are almost as helpful; a cameo can gin up profile and stir-up attention, but not necessarily bring back favor. Ms. Spears proved that for a few minutes she can play someone else. But she was not entrusted with an opportunity to show she is herself again.

“How I Met Your Mother” was not an indicator that Britney Spears is back. At best, she is on probation.