Please take reference from this question. It is said in RFC 6864 that if IP V4 IDs remain unique during MDL, it would limit speed to max 6.4Mbps. Now high speed devices generate data at a much higher rate than this.
Suppose a packet with ID X generated by host A to host B gets splitted in 3 fragments: X1,X2 and X3. Say X1 and X2 get delivered at B but X3 is stuck somewhere. After sometime host A again delivers another packet with same ID X, which again gets fragmented into 3 fragements: X1',X2' and X3'. Now suppose X3' gets delivered to host B earlier than X3.
Then in this case wrong data shall be assembled and transferred to upward layers. How is this problem being taken care of in today's world in IPv4?