In 1990, fifteen VFKX wagons were modified and converted to VQKX.
There are two number groups in the conversions. VQKX 1 - 8 were converted between April and July 1990. VQKX 100 - 106 were converted between July and September 1990.
Difference in the two groups is not known by the author.
In 1991, VQKX 4, 8 were converted to VEKX 213, 214 respectively.