NOTE: Nearly all users should only ever need to have one version installed - either the current one or the last one available when their free upgrades expired.
However, occasionally it can be necessary to want to have two versions installed at once. A good example is assessing a new version to decide on purchasing an upgrade after having let cover lapse. This approach is also needed for beta testers.
So, it is possible, but do so with care. It is not a supported form of general use. Both versions will share the same app settings.
Do not try to open both versions at the same time - you will not get a warning (or a crash) but you may get unexpected results, so do not do it!
It is suggested to leave the current version of the application installed in Applications. This user then places secondary versions on the Desktop, or whatever location is chosen. If wishing to keep multiple version in the same folder, one will need renaming before being added to the folder.
As all installed versions share settings file, if using a much newer version for test, there is a chance the settings may not then work in the older version. This has not been seen, but if it does old app setting may be lost. Plan accordingly.
As aTbRef's author is also a beta tester, this document has been used editing on multiple versions of Tinderbox (albeit one version at a time) including most betas and without harm.
Note: it is worth repeating that very few users will ever need to use this configuration, but it is worth documenting for those who do.