In further examination of this website,
TikiWiki : Cavitation - The Complete Guide I find incorrect information. Allow me to explain how I can determine this. If you read my bio, I am a field service engineer with Cummins (Fleetguard business unit). I work with coolant and chemicals as well as our filter products. My specific area of support is to the end user and OEM customers on issues of product application engineering, maintenance training, failure analysis and maintenance consulting.
Statements made on that web site about compatibility of SCA are at best, uninformed. There are no issues with mixing supplemental coolant additives In the standard SCA products there are two categories; nitrite and nitrite/molybdate. Sorry for the chemistry lesson but when you deal with coolants you are specifically involved in chemistry. Regardless of brand, all SCA products do mix and have no issues with chemical reactions. Statements made by manufacturers about compatibility issues of SCA and engine coolants are made by the Marketing and Sales divisions to promote their products and discourage (scare) you from mixing or leaving them. Their hope is that making changes in your coolant product usage will be so painful that you will not change.
For the record, Fleetguard DCA4 IS Ford FW16 later VC8. Napa SCA will be either of the two types listed above. You could mix DCA4 (ntirite/molybdate) with Napa or Penray Pencool or even Baldwin BTE additives. While DCA4 has two cavitation protectors, these others use nitrite only. No issues with mixing. Fleetguard offers the same nitrite only SCA, DCA2. Same story for engine coolants. Manufacturers of OAT coolants (organic acid inhibitors) started out by making dire warnings about mixing. Later after customer backlash, they toned down their rhetoric on that topic. Unfortunately, those early statements are still being passed around as 'fact'. "Thanks, Internet!"
In reading further, that website assumes that products like DCA4 came about because they are better than earlier SCA products like DCA2 or Pencool, Nalcool additves. The short answer is that due to the sales promotion of the earlier SCA like Nalcool those additives were over used. That was due to the promotion that if "some is good, more is better". True, up to a point. In the matter of DCA2, Nalcool, Pnecool and similar nitrite-only additives, these products continue to provide solid protection but the user should be cautioned about over concentration. This last issue resulted in heavy corrosion of lead solder in copper radiators. DCA4 and similar products reduced the solder corrosion aspect of over-use by substituting some of the ntirite with the sodium molybdate additive. It gave better cavitation protection while actually using less additives and greatly reduced solder corrosion issues. Baldwin, Donaldson, Fram and Wix/Napa offer DCA4-like SCA.