Need help recovering Resmed A10 sdcard data

[epc002]

I have a Resmed A10 bilevel machine, new in 2020-11-08, using the original Resmed 4gb sdcard that came with it.
Every month or so I import the sdcard data into Oscar, and every few months I make an archive zipfile of the sdcard.
Everything's been working fine until 20230630 when I went to import the card into Oscar, only to discover that there is no detailed data (in the card's DATALOG dir) for any dates prior to 20230629.
I recall when I did the import on 20230610 I noticed that the card was nearing it 4gb capacity.  Now it's got a lot of free space.

First question is, does Resmed automatically delete all files on the card and start over when it reaches capacity?

Anyway, after recreating the DATALOG entries from backups and oscar profile backups, except the missing 11 days, I made a new 32gb sdcard with all the files, and it imported successfully into a test profile in Oscar.
This 32gb will be my new Resmed A10 card going forward.

i then attempted to recover the missing 11 days of DATALOG data, by using Recuva file recovery software on the original Resmed 4gb card.
It did find the .edf and .crc files for those 11 days(and everything else), and I restored them to a test dir on a sandbox system, and used a script to place the files in the appropriate  yyyymmdd subdir structure.
I then made another test sdcard by direct copy of the original Resmed 4gb sdcard, and added the data for the missing 11 days into the DATALOG dir.
I created a test profile in Oscar and imported the sdcard into it, it appeared to import successfully, but the Oscar graphs for those 11 days are clearly bogus.
The files also import ok into Resmed's ResScan7.0.1, but the graphs there are also way off.

Second question is what to do to get the recovered DATALOG files to correctly graph in Oscar, and what would be the reasons they do not display correctly?

[srlevine1]

It is my understanding that your SD card only contains 365 days of summary data and 30 days of detailed data, and if you want to preserve that detailed data, you need to download the data before it rolls off the file and is overridden. The amount of data stored on the card is independent of the card's size, therefore, a larger card than what ResMed typically includes with a device does not appear to convey any particular advantage.

What I do is import the SD card data into both Oscar and ResScan about every 25 days. If I wanted to back up the raw files from the SD card, I would do it at the same time.

Recovering erased files and putting them back into a current folder does not appear to work to produce valid imports of the erased data. Possibly due to a mismatch of crc codes protecting file integrity.

Did ResScan download more than 30 days of detailed data, and did ResScan ask you if you wanted to overwrite the duplicate data?

[pholynyk]

To answer your first question first, the answer is yes, the machine erases the old data and starts over. From your ability to recover files, I would guess it simply writes an empty root directory over the old one.

I'm afraid I can't answer your second question...

And to correct srlevine's understanding, the machine will save up to one year of summary data internally; if you insert an empty SD card, it will write all that to the STR.edf file. No detailed data is saved internally, and it will add detailed data to the SD card as long as their is space available. It won't lose detailed data until the card is full.