Thanks to everyone for their comments and suggestions. Here's what happened in the end. I will put all the details so the pluses and minuses are clear (based on my experience - YMMV).
I arrived at DPS airport 2 hours before the 00:45 departure time. I should have arrived 3 hours earlier to make sure I had some Garuda lounge time!!!! I went to a SkyTeam priority checkin counter, but the guy indicated that there was a Biz checkin counter somewhere else. I was happy to stay and let him deal with the issues. At first he said that you're traveling only to NRT, so you'll have to collect your bags there and check them in at JAL in NRT. I said that I had emailed with Garuda customer service and they put a note in my record that I was connecting, and that it wouldn't be a problem to check my bags through to DCA, and that Garuda could interline them. I showed him the response from Garuda customer service and he read it. He then looked for the note in my reservation. I think this was crucial for success.
A conversation then ensued between him and someone senior in Indonesian (or Balinese, not sure
), and I heard the word "interline" and "customer service", and the guy took my phone and went and talked to someone. He came back and said they could do it. He asked to see my JAL boarding passes (I had done online checkin with JAL and had PDF boarding passes on my phone - I did not print them). He also looked at my printed itinerary on JAL which I had taken with me to DPS. It showed my ticket number.
The agent slowly typed in the connecting flight information He asked me what the code was for Chicago (ORD
and then for Washington (DCA). He was extremely pleasant throughout this experience and wanted to help. Maybe it would have been even easier at the business checkin counter, wherever it was. After keying in a lot of information at his terminal, he finally produced 1 Garuda BP and attached to it 2 baggage tickets all the way through to DCA showing the relevant flights. He then asked for my passport and went off to talk to someone else about the whole matter. I was worried at this point there would be a problem.
He came back after about 10 minutes, returned my passport to me, the BP and the baggage tickets, and asked me to sign a waiver (see image below). After I signed, he gave me a copy and I left. This whole process took about 40 minutes, and because I had not arrived earlier, I had no Garuda lounge time in DPS. The Garuda flight was really nice. I have never flown on them before. Seat very good. Service great. Food very good. Arrived in Tokyo earlier than expected. Some things that happened at Tokyo were not expected.
Before exiting the plane, I was paged by ground staff on the plane PA system. My name + my connecting flight info JAL 10 to ORD. They advised me to see ground staff after exiting the plane. I was worried something bad was going to happen
Upon exiting the plane, there was a woman standing with a sign with my name on it. I identified myself to her and she told me where I should go to get the bus to go to the JAL terminal, and that I should go to the transfer desk and get new BPs (and not use the BPs on my phone), and that was it. I went to the transfer bus area near gate 28, and I was surprised to see the bus only operated every 30 minutes. I will attach a picture of the bus timetable later. This meant I had to wait about 25 minutes for the bus as I had just missed one. Nothing to do about this, but it's good to know in terms of planning connection times. (Edit: frequency seems to increase in the afternoon to less than every 30 minutes - see photo in next post).
Bus finally arrived and I went to T2 and easily found the international connection desk. I showed the women the BP on my phone and she said, "We were expecting you." I saw a printed itinerary with my name on it next to her computer monitor. She took my phone, my passport and asked to see my baggage claim tickets from Garuda. She said they needed to do the checkin again, and they did. She confirmed that I had checked two bags. She asked if I have visited China in the last two weeks. She finished the checkin and returned the baggage claim tickets to me and gave me 2 BPs, one for JAL and one for AA. And that was it. I went to the Sakura lounge for about 45 minutes and then got the flight, where I'm writing this review now.
It all worked out, and I was impressed by the level of service in DPS and NRT, but I definitely wouldn't count on it always being like this. I think emailing with Garuda customer service was the key to success in DPS. And I should have arrived earlier at DPS. Thanks again to everyone for making suggestions and advising me about the potential pitfalls.
A note on the JAL flight. Great Japanese food. Seat seems very comfortable (window seat in C - 12K). IFE has a strange glitch which causes the films to pause momentarily every few minutes. But I'm happy with everything on this return trip to the US so far. Let's see how the connection goes in ORD and the flight for ORD-DCA. If the bags don't actually arrive, I will certainly add that detail
Status of bags: they arrived OK in ORD on same flight as I did. Apart from the usual tags for priority pax, there was a "TRANSFER" tag on both bags from Garuda. I'll send a photo after the trip is over. Glad to have my bags! PS: AA lost one bag from ORD to DCA. It is being delivered on a later flight.