Near the end of "First among Sequels", Thursday1-4 goes to the real world illegally.
In "One ouf our Thursdays is missing", Thursday5 needs to go to the real world, but she can do so only by using a technological device. Even then, when she is in the real world, she has a lot of difficulty adapting. The scientist who made the device gave her a lot of instruction, and still she found it difficult to stay there. She was also on a time limit.
Although Thursday1-4 is more capable than Thursday5, she should still encounter the same difficulties, and unlike Thursday5 she had no-one to prepare her. She just went there, and seemed to have no problem staying until the original Thursday showed up to set things straight. There was no talk of a time limit; if there had been, it might have influenced the original Thursday's strategy.
So how could Thursday1-4 go to - and stay in - the real world so easily? When in the next book that was explained to be very difficult?