Yes, the NRLC in part endorsed Thompson because they believed he could win the nomination. Since then though, several other pro-life groups have endorsed Fred, even as he slipped in the polls, including the SC pro-life group. Fred's 100%pro-life record is the reason, and Romney's road to Ames conversion is the reason they held back on endorsing him.
We'll see what happens in SC. He will likely do much better than you think he will. If he doesn't, the NRLC might endorse Romney, but only because Rudy is obviously pro-choice, and Huck and Queeg are complete lunatics. They will be holding their nose as they make the endorsment just as many will hold their nose to vote for Romney in the general.
I'm just perplexed by the SC group. Fred just isn't pro-life by any definition. Supports no restrictions on any abortions apart from voting for the PBA ban when he was in the Senate. Opposes human life amendment. Opposes any state level restrictions though he supports the right of states to make those restrictions.
If they were making their endorsement after IA, they would have endorsed Huck, and given they are a single issue lobby, I would have at least understood that.
Queeg isn't prolife at all - he opposes overturning RvW.