EDIT: it also may be possible in your case that the dash cam in your vehicles are keeping small loops of video in temp storage/RAM, and only recording to the card when saving a segment for long term (I.e. During a crash event).
No mine do not have RAM or internal storage. If the card is out it does not work. I believe the vast majority of cams do not have RAM.
In many EU countries these dash cams are now normal thing to have and imagine the mount of SD cards being used in them.
Also many cams have both front and back camera and write 2 , high bitrate, 1080p or some even 1440p streams on these cards at the same time and last for years and years in the sun and cold of winters no problem.
I have been reading forums about cams and complaints for the SD cards dying are only related if the cards is no-name no-brand or some suspicious way they got it.
Samsung and Sandisk cards are immortal.