The BLS has been fudging unemployment numbers for a long, long time now. The idea here is to keep the headline number under 400K, which would be seen as a big red flag. Of course, this week's number will in fact be revised upward next week to something over 400K, but by then, the headline will be forgotten.
The claims number is nearly always revised upward, something that you might find amusing if you know anything about probability statistics. Try running a binomial distribution (coin flip scenario) to see what is the probability of a previous week's number being revised upward 51 of 52 times, as it was last year. The result includes a decimal point with a whole lot of leading zeros....
If I'm remembering my statistics correctly, the probability of a coin flip coming up "heads" 51 out of 52 times (which as you say is comparable to the numbers being revised upwards 51 out of 52 times.....) is 1 in approx 2.2 Quadrillion.
You'd be thousands of times more likely to hit the Powerball.