Why was Andy Murray allowed to play doubles in Washington without a wildcard or PR?

Question

At the Citi Open in Washington 2019, Andy Murray played doubles with Jamie Murray. The team did not got a wildcard, nor was it a protected ranking (PR). Link to draw.

According to this answer on sports.stackexchange.com, the ranking 6 week before the tournament is relevant for enter a draw. Andy Murray did not have a ranking 6 weeks before, according to ranking history

In the draw it is mentioned, that the last direct acceptance are "Advance-47/On-Site-54". Why was he allowed to play doubles in Washington without wildcard or PR?

Edit:
I found something in the rule book, page 10 about commitment player:

C. Commitment Player
A 2019 ATP commitment player is any player positioned in the Top 30 in the ATP 2018 Rankings (singles) as of November 5, 2018.
...
E. Commitment Player Entry Exception – Top 30
Commitment players are automatically accepted into the main draw of all ATP Tour 500 events in which they have entered in a proper manner.

Commitment players only are single players. Does this count also for doubles main draw?

Answer 1

For entry into ATP doubles draws, the singles ranking can also be used as per the following rulebook section.

VII The Competition / 7.13 Selection of Entries / C. Doubles Main Draw - ATP Tour / 1)

Andy Murray henceforth used his Protected Singles Ranking for entry into the doubles draw as per the following rulebook section.

IX. ATP RANKINGS / F. Entry Protection / 3) Limit of Use / a)

Answer 2

I was able to find some clarification on the rules in qualifying, though not specifically for this event. The key part that helped me track this information down was the "Advance-47/On-Site-54". Based on the information from this document(page 93-94), there are qualifying places designated for those who have signed up for the alternate list for a given tournament. Additional places are made available when other qualifying teams withdraw prior to the start of the qualifying rounds. There's a lot of solid information about qualifying in section 7 of this document.

B. Main Draw Doubles

1) ATP Tour Tournaments

a) Advance Entry. 12 Noon, Eastern Time, USA, fourteen (14) days prior to the Monday of the tournament week (or the first tournament week in the case of tournaments scheduled for more than one (1) week). A team on the alternate list for the doubles main draw may withdraw at any time prior to such time 94 VII. THE COMPETITION that they are moved into the main draw as a direct acceptance because of withdrawals of other teams.

b) Withdrawal Deadline. The deadline for a team to withdraw from the advanced entry list closes at 12 Noon, Eastern Time, USA, on the Friday prior to the tournament week.

c) On-site Entry. The period for online on-site entries opens at 12:01 am, Eastern Time, USA on the Friday prior to the tournament week and closes at 5:00 pm Eastern Time, USA on the Friday prior to the tournament week. The online sign-in is blind and no preliminary lists will be produced. Players entering multiple events in the same week must do so with the same partner and shall designate tournaments by priority. The number of places available through the on-site entry is specified in the Composition of Draws (7.08.B) plus any spots made available through withdrawals occurring after 12 Noon Eastern Time, USA, on the Friday before the event week.

d) Limit to On-site Entry. A team is allowed entry through the on-site entry method a maximum of two (2) times per year in events where they would have been accepted, using their doubles ranking, on the original list in that event through the Advance Entry system, if they had entered.

Another point worth considering -- I found this quote from a New York Times story on his return to play. Probably helps to call the owner directly to secure your spot in the qualifiers.

“They called us and said Andy really wanted to come back to D.C., and wanted to play doubles with his brother,” said Mark Ein, the new owner of the tournament.

Further, the Citi Open website clarifies the numbers of each type of qualifiers.

Main Draw Doubles Direct Acceptances: 10

Teams Wild Cards: 2

Teams On-site Entry: 3

Teams Qualifying: 1