The direct answer to your question is that based on a recent change in our policy, the two operating systems you mention no longer have “Mainstream” support from Microsoft. See: Windows 8.1 and Windows Server 2012 R2.

Microsoft’s support is our reference point for the operating system support we publish with each DataFlex revision. As of DataFlex 19.1, we have changed the scope of operating systems we support as of a revision’s release. Previously, without considering the consequences, we did not discriminate between Microsoft’s Mainstream and Extended Support as defined in their Business, Developer and Desktop Operating Systems Lifecycle Policy. If Microsoft published either Mainstream or Extended support for an OS, we stated support for it too as our releases occurred. A recent forum post caused us to examine the implications of including as a supported DataFlex OS everything that Microsoft supports.

Without having the distinction of two levels of support like Microsoft’s Mainstream (5 years) and Extended (10 years; some of the Extended benefits are fee-based), our support for operating systems published as of a particular DataFlex revision could cover their almost 10-year-old products. For issues relating to a DataFlex revision and the underlying operating system, we consider 5-year OS coverage to be sufficient, so our policy is now to publish a new DataFlex revision’s operating system support only for Microsoft’s then-current Mainstream supported operating systems. That doesn’t mean that a new DataFlex release will not run on an Extended support Microsoft OS; it does mean that we do not test on Extended support operating systems and do not address issues that may be encountered on them. Validated issues in supported DataFlex revisions that occur on a supported OS are logged as candidates for fixing in a future release as defined here under “How Bug Reports are Managed”.

In practical terms, there is little impact from this change when it is looked at from the perspective of our support policy in general. As defined on our Current Products List, “For customer support purposes, a "Current Product" is the latest release and the two prior releases as listed below...” – unlisted DataFlex releases aren’t supported anyway regardless of the OS. With our releases occurring approximately yearly, general support for a given DataFlex revision will typically lapse well before the end of even Microsoft's Mainstream support. Currently, the oldest supported DataFlex revision is 18.1 (released July 2015) and it will be removed from the list as of the upcoming release of DataFlex 19.1.

Finally, a change to an OS’s support status by Microsoft or Data Access does not, on its own, necessitate customers upgrading their operating systems although staying current is always advisable. There are lots of DataFlex applications running successfully on Extended support OSs and even unsupported OSs. If there are operating system security issues during the Extended support period, according to their policies, Microsoft continues to publish operating system updates for the benefit of DataFlex applications of any revision and all others running on that release.