Hi John,
Technically they should sync the sessions, SA and other important information. However, you may see configuration out of sync errors as both the codes will be have different hash values. Different versions on the devices is strongly not recommended.
Please refer https://kb.juniper.net/InfoCenter/index?page=content&id=JSA10713&actp=search vulnerabilities, due to which you will not see 6.3.0r14 and many other codes on the website.
Thanks,
Vikas