I'd assumed the dash clock on my car was RDS driven - since I've never needed to adjust it in the 6 months or so I've owned it. Always clicks over with the pips on R4 FM. Info page on the radio also shows the same time.
But it didn't reset at the end of BST. Set it manually roughly, two minutes out. And was surprised to see it click over the minute with the pips, again exactly, but two minutes out. Like it is synced to RDS, but only partially.
Or perhaps the sat nav? But most I've seen give you the option of +/- and hour - not minutes?
I've not looked into how the time is encoded into the RDS signal but, while I would expect there to be error checking (possibly even correcting) in the coding, it isn't impossible for these techniques to fail. As you may know, if error checking is used, the message must 'follow' a set rule. Therefore there are a finite number of valid messages. The the invalid ones are in the gaps - the concept of Hamming Distance, the fewer valid messages, the greater the gaps, (larger Hamming distance) and greater protection. However, there is an overhead, as you make the code more complex, it increases the bandwidth needed.
If you get a valid code, even if it is actually wrong items of being corrupted, the system can't tell. While that could explain what you've seen, without a lot more data and work, it would be hard to verify.
In more complex systems (and I don't know if this includes RDS) even more bits (data) is added which can be used to correct detected errors. However, even then, only if they are detected- back to the Hamming distance.
(I was an engineer in a previous career and digital data transmission 'featured' all too often. ;-) )
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