At the outset, I should say that I have never had the privilege of managing a 4 "Day 1" event, so I can only tell you what I think should be done. If I am wrong in my opinions, I trust someone will correct me.
With respect to the bagging and the redraw, first, it should be possible to write on the bag, at the minimum the player's name and chip count.
Second, I would consider having players fill out a receipt, preferably that makes three copies: One for the dealer, one for the player, and preferably one for the bag. (Sometimes you can get away with not having a third copy for the bag, if you get players to clearly write all the information on the bag itself.) The receipt should have a place at least for the full name of the person, their hometown/country (in case two people have similar names), and chip count. (Note that the chip count is not binding and the floor/dealers will not verify the counts... it is effectively only an estimate. The player is only entitled to whatever physical chips have been sealed in the bag.)
At the end of each Day 1, you can then collect all the dealer copies of the receipts, and use the receipts (not the bags themselves) to start entering information into the computer. Meanwhile, I personally would store the bags in a safe room, but instead of dumping them all into one big pile, I would have someone sort the bags into different piles alphabetically by last name: e.g.. after Day 1A, throw all bags for players with last names starting with A-C into one pile, D-F in another pile, etc..; and after Day 1B, just add the new bags to the appropriate existing piles based on player last name. (I don't really see any benefit to sorting the bags by the old day 1 table number).
At the end of Day 1D, after you've finished entering the remainder of the player information (from the Day 1D receipts) in the computer, you can now create your new seating lists for day 2A and day 2B seats. This should be done by using a random draw from all the names of all four days combined. The list can be posted in the room, on your website, in the lobby, etc.
At the very beginning of day 2A before play begins (or better yet, you can start the night before), you will need someone to take the new seating lists, and retrieve all the bags for each Day 2 table. The person will find all the bags for Day 2A Table 1, by looking in the pile of bags based on each player's last name. Optionally, you can also have someone write the new table number on the bags with a marker. The bags are then found for Day 2A Table 2, Day 2A Table 3 and so on. Repeat for all Day 2A and Day 2B tables. If everything goes well, all bags for all players on the list should be accounted for (if not, you will have to determine why there is a discrepancy, whether it is because you are missing a bag or you have an extra bag or whatever). It is a bit of work to sort all the Day 1 bags into new piles for the Day 2A & Day 2B tables, but if you were disciplined enough to take the time to sort the bags into piles by last name after each Day 1, it should not take too long to find all the players' bags for the new tables. Once all the bags are sorted by Day 2A & Day 2B tables, then you simply need to bring them out to the tables when the dealers are seated. And I think that's it.
I would tend to do the redraw as noted above. However, I should point out that there are other ways of doing the redraw. For example, I believe at some events, the receipts that are filled out by each player at the end of day 1 may have Day 2 seating assignments already pre-printed on them. For example, a stack of receipts each with a pre-printed Day 2 assignment "table 1 seat 1", "table 1 seat 2".... "table 50 seat 7", "table 50 seat 8" can be generated in advance based on an estimate of how many players will make Day 2. These receipts are then handed out "randomly" to different Day 1 tables. Some TDs may decide to have seats 1 & 2 for each table reserved for Day 1A players, seats 3 & 4 for Day 1B players, seats 5 & 6 for Day 1C players, and seats 7 & 8 for Day 1D players, or some similar breakdown, so that different players from different days will be mixed up at any given Day 2 table. The good thing about this method is that you are effectively doing the redraw in advance by using pre-printed table assignments on the receipts, and players will already know what table and seat they are going to be in when they leave for the day on Day 1. And since the Day 1 bags can be marked with the Day 2 seating assignments as shown on the receipt, the bags only need to be sorted once, by Day 2 table, for storage.
However, the problem I have with using the pre-printed receipts is that it is not truly a random draw. One doesn't know how many players each day will end up with (e.g. what happens if you have a lot of players left after the same number of blind levels on Day 1D and you need more receipts?), and a random draw should allow for the possibility of different numbers of players from different day 1s to be seated at any given table.
For a redraw to be truly random, in my opinion, one should wait until the end of the last Day 1, and then do the redraw with all players left from all Day 1s combined. That is why I personally do not prefer the pre-printed table assignment receipts, and opt instead to the redraw in the manner I outlined earlier. Sorry for the long post... I hope this is helpful.