However, there is nothing to prevent a state from petitioning for a general convention at which any subject could be considered. There are two petitions on record from 1789, although Congress would no doubt say that those petitions were "stale". But even the ABA understands that a general convention is possible. Note, however, that a general convention cannot write a new constitution, only formulate amendment proposals on any subject it pleases.
In Walker v. US in 2000, William Walker asked the federal courts to consider that Congress should have called a convention back in the 1890's when the two-thirds threshold was first reached. Judge Coughenour dismissed the suit stating that Walker lacked standing. No state has gone to court to make the same claim. This is because the states recognize both the Single Subject Standard and the Contemporaneousness Standard. The Single Subject Standard, at least, has roots in settled contract law, and both the states and Congress understand that an Amendments Convention is bound to its subject by longstanding principles of contract law that even predate the Constitution itself.
To prevent Congress from using specious excuses like word difference and punctuation to prevent petitions from being tabulated in the correct column, the ABA went so far to suggest that each state sending a convention petition to Congress say in that petition which states had previously submitted petitions on the same topic so as to force Congress to tabulate them in the correct column. The reason the movement is calling all these preparatory sessions is to work on the wording so as to prevent Congress from refusing to call a convention because of specious excuses about words. They are also working on the ground rules so as to prevent Congress from passing any bill like those earlier written by Dirksen, Ervin and Hatch that would exercise the wide latitude in regulating the amendatory process that Congress got from the Supreme Court in 1921 and 1939. An ounce of prevention in worth a pound of cure.
The Assembly of States meet in a couple months, June 12th in Indianapolis. I like to think they have, or will, consider the best, most foolproof approach.