Assuming that by "QlikView Client" you mean the QlikView Desktop which is mainly a development tool, it is generally considered a bad practice to use different versions of the core products. By different versions, I mean QV11 Desktop and QV12 server or vice versa. Different Service Releases in the same main release won't do much harm, but should be avoided as well. Simply because support on homogeneous product combinations will lead to faster problem resolution. The main pieces of advice are:
- Use identical versions for QV Desktop and QV Server (this includes the Publisher). Connectors lead a separate life, and NPrinting versions should be selected based on their compatibility with the main QV release.
- Upgrade to the latest Service Release as quickly as possible (however ... see below). You can test new Service releases by installing and using a newer QV Desktop first and verifying that critical document operate without issues, before upgrading the server.
- Always consult the Release Notes. If the fixes that are listed in the release notes don't bring much added value to your environment, consider delaying an upgrade if upgradng is an expensive affair.
- Avoid upgrading complex architectures on the same day of a new product release. If a release contains unexpected issues, they will be posted on Qlik Community within days.
As for your other suggestions: the QVW file format (still compatible with QlikView v7) used to make life simple. Older versions of QV Desktop cannot create or edit new features, so editing a new file with an older development tool is not guaranteed to bring much joy. But it won't destroy your work. The reverse (editing older documents with new Desktop versions) will be mostly ok, but there may be differences in behavior and performance between v11 and v12 (caused by the switch to the Qix engine)..
