Just in case you missed it last night:
The T/A and MELY have no idea who owns shares, unless they were issued in certificate form. The rest of the shares are in street name of CEDE and they change all the time. Again, the brokerages are the only ones who know who owned shares on the record date. No NOBO list or OBO list is up to date so the system is simple. The brokerages are notified of the divy and the qualifications to participate in the dividend. The brokerages go to the accounts, make sure they qualify and then send the request to the T/A. This is done in a simple confirmation program the brokerages use by setting the perimeters of the qualifications against the CUSIP number. The program spits out the number of shares that qualify and what account qualifies to receive the dividend shares when the brokerage house receives them from the T/A. The T/A sends the brokerage house the shares necessary to fulfill the brokerages clients account. It is done electronically and is a simple process. The question is 'when' does the brokerage house notify the T/A and 'how long' does it take for the T/A to process the notification and send back the shares.
The Reverse Split shares are treated in a similar fashion but some brokerage houses will allow the account holder to trade their shares with a phone call so the brokerage house can warn them that they are selling the stock short and if the share exchange does not occur then the client is responsible to cover the short position. This never happens with today's electronic systems. Again, it depends on how quick the brokerage houses send the request to the T/A and how quickly the T/A responds. That is why different brokerage houses handle corporate actions in different time frames.