"Why wasn't there a further card for Guimares after having been shown the RC as he obviously said something to Tierney given Tierney's facial stunned reaction?"
Anything he said can be reported but I dont think you can be shown another card after a red?
Let's hope that it was reported and an additional ban follows. Having said that; and given the current approach to "managing (=tolerating and tacitly encouraging) such situations, I am not holding my breath for this to happen.
PS: It should not have needed VAR to point out to an SG1 referee that an act of SFP had taken place some 5-10 yards in front of his unobscructued view.