Testing of Replicants throughout the various eras has changed relatively little.
Replicants in these classes are relatively easy to detect because they're obedient, don't look very human and aren't especially bright. At some point they start getting smarter and the Voight-Kampff test is introduced in order to replace bone marrow testing in those rare cases where a Replicant can't simply be spotted by a trained individual. In the original novella, there's also something called the Boneli Test that may or may not be effective.
These Replicants are smart and capable of fooling sight-testing. The VK test becomes streamlined and mass testing becomes possible by a trained operative. Blade Runners are also generally capable of spotting a Replicant by sight alone, through personal experience, but prefer to have VK proof before retiring them.
Practically human Replicants in this class can still be detected by VK testing (albeit with much greater difficulty) and bone marrow testing and at autopsy.
Nexus 8 (Legit)
These models were placed onto a database and had a standard eye implant that made their detection simple. After the Blackout event, their detection was much harder but they would often give themselves away through their actions such as superhuman strength, resistance to acid or heat, etc. As above, intrusive testing would also work.
Nexus 8 (bootlegs)
As above but minus the eye implants, these models were very hard to detect and Blade Runners largely need to rely on personal experience and intrusive testing.
These models typically have an eye marker and are obedient to their human owners. Baseline testing is used to identify when a Replicant is becoming unstable rather than to detect whether the individual is a Replicant. These Replicants are loyal and obedient, which means that they don't need to be detected by Blade Runner units.
It seems highly likely that the rogue Replicants in this RPG will be legit Nexus 8s that are on the run after the Blackout. Blade Runners in this era use a combination of police work and refined observation to detect probable Replicants and will retire them on sight if they're certain that they're dealing with a skinjob, or capture them for lab analysis if they're uncertain.
...everybody knows the law just walked in. And means business. As a
walking Voight-Kampff machine, you’ve made a career out of pushing
people’s buttons and getting to the core of who (or what) they really
are. Looking where you shouldn’t. Going where you’re unwelcome.
Blade Runner - The RPG Core Rulebook "Inspector"