Life Master Specification

its not cumulative games if you drop below then it resets.

you can also gain a master norm by making a 2200+ performance +1 point in a tournament. harder than it seems. 

i think both systems are in place still. The old life master norms were the 300 games which was very difficult but it had a secret one that was 3 tournaments with a performance rating of 2200. A lot of people abused this and it was taken away the new one is quite difficult. since it basically requires a better than average result. NOt sure if there is a time limit for the norms though

Okay, there are/were three systems:

First, is the "Original Life Master" (300 games with a post-tournament USCF rating of 2200). As PaulEChess said, the count is cumulative (in fact, you can find out exactly how many games you or anyone else has above 2200 by searching for a player on uschess.org under "Players and Ratings" on the left sidebar). Once a player reaches 300 games, they get a floor of 2200. This is the ONLY way to get a 2200 floor: you could be rated 2600 USCF, but if you haven't played enough games (i.e., more than 300), your floor maxes out at 2100.

This system is still in use and is considered the most prestigious, and you get an Original Life Master certificate.

Second, was the (first) Life Master norm system. You could get the Life Master title by scoring a performance rating of 2500+ in one shot, for example (I know a player who achieved this). This system was in effect during the mid-1990s or thereabouts, and I'm not exactly sure when it ended, but it doesn't exist anymore.

Third, is the (current) Life Master norm system. This is actually quite a strong achievement: unlike the OLM system (which rewards consistency), this system rewards very strong results. If, given a certain set of opponents in a tournament, a 2200 player is expected to score 2.5 points out of 4, then a norm will be awarded if the player scores MORE THAN one point higher than the 2200 expected score (i.e., greater than 3.5 points). In other words, the player would need to score 4-0 to be awarded the norm!

A player must earn FIVE such norms (and have achieved a 2200 rating at some point or other) to be awarded the (new) Life Master title. This norm does not earn a 2200 floor, but you get a Life Master certificate. There is no time limit for the norms.

So systems 1 and 3 still exist. Also, you are supposed to get a certificate for National Master once you clear 2200 (even if it's only briefly).