What happens, when you use an "old" piwik.js for tracking with a newer piwik version

We are caching piwik.js for page loading porpuse. So, when we upgrading piwik to the latest version, it could be possible that an older piwik.js will be used for tracking in a short period. Are there any possible known side effects? Like missng tracked visitors or features dont work correctly?

We highly recommend to always update piwik.js to latest version because we sometimes fix bugs there. But it will still work anyway if you use the old one for a few days. Just upgrade it ASAP

Ok thank you.