The seven-octet Preamble comes after a 12-octet (or longer) Inter-Packet gap, then you get the one-octet Start of Frame. Next, you get the ethernet frame header with the destination MAC address, source MAC address, etc., followed by the data and the Frame Check Sequence, then the 12-octet Inter-Packet gap.
There is no way to confuse data in a frame with the preamble because there would be no Inter-Packet gap. Also, unless the destination MAC address is a group address to which the interface has been configured to listen for, all the interfaces other than the destination interface will ignore the rest of the frame.
Edit per your comment:
An Inter-Packet gap is 96 bits of silence on the line, but a frame has no such thing because a frame is sent complete from start to finish. It would simply be a damaged frame if it stops before the end, and there would be no FCS, so the last four octets would not match what the FCS should be. In fact, the frame could be too small to be valid.