Bear in mind that nearly everyone who wanted an entry to PBP 2019 got a start: maybe they needed a 200 BRM in 2018.
I don't think that's strictly true, there was a massive row about places running out in the people who had only done a BRM300 in 2018. so those with only a 200 or no ride at all could not pre register.
Places did subsequently become available as people failed to complete their 2019 SR series, but by that time some of those that had failed to pre register had not started a 2019 BRM series.
This time there are more places available, and there may be more scrutiny of qualification from countries with a poor completion rate.
Off topic (a bit) ACP required one to pre-register from January onwards ( >=1000, 600, 400, 300, 200 in fortnightly intervals)
"Preregistration will be open from 14 Jan to 24 May to all riders who successfully completed a BRM [or LRM, in previous 'year']. [Will] reserve a place for the PBP 2019, as far as there are enough available places. . . . convert your preregistration to a final registration before 20 Jun.
And here's the ACP announcement:
http://www.paris-brest-paris.org/index2.php?lang=fr&cat=accueil&page=dernieres_nouvelles (after a serious brouhaha Francais) to allow the BRM 200 riders in:
"April 10th, 2019 - maximum number of places has be[en] reached
. . we have increased the maximum number of places from 6700 to 7600. This was made possible through the effort of the start-finish and stages towns to welcome as well as possible thousands of participants. We have made overbooking to take into account the number of defections, . . . ."
All those who had a 200 in Nov 17-Oct 18 got a start (aka could pre-register from 10 Apr onwards) if they wanted one.