Is there really any difference between Resonance and Mesomeric effect?

I have been in the classes of two different teachers of organic chemistry and they both agree on the fact that there is a difference between the mesomeric effect and resonance effect (they didn't agree mutually, I just compared their answers) but both of them tell the differences which are unique or simply don't match. So I decided to find the difference via research. I searched online and in the books but answers there also vary. Here are some findings of my search

1. Answer by @NotEvans (here) mentions that in the gold book of IUPAC, they have been taken as synonym terms.
2. Answer by @Raju (here) mentions the difference as "Resonance refers to delocalization of electrons in a given system. The mesomeric effect is the electron-donating or withdrawing nature of a substituent due to resonance." The answer matches @KshitizSharma answered on the link where @NotEvans answered.
3. A page on the website Pediaa mentions the difference to be "Resonance is the effect that describes the polarity of a molecule that is induced by the interaction between lone electron pairs and bond electron pairs. The mesomeric effect is the effect of substituents or functional groups on chemical compounds."
4. There are several other places but as expected, all their answers differ

My one teacher let's say A (don't want to disclose the name) says that the Resonance effect is a broader umbrella term that includes the mesomeric effect. In resonance, we have delocalization of electrons and the delocalization can be of several types such as pi-electron delocalization, sigma electron delocalization, dancing resonance, etc (these phenomena are shown in images below) but in mesomeric effect, we can only have pi-electron delocalization.

Dancing Resonance

Sigma Bond Resonance

Pi Electron Resonance

Now my other teacher, let's say teacher B sort of agrees with the definition and difference of Resonance and Mesomeric Effect given on the website Pediaa which is mentioned above in point 3.

My opinion (not conclusion) on all of this is that technically my teacher A seems to be correct to me. But I can't decide and the definition on the IUPAC book confuses me even more so I came here to ask for help. Thanks.

Notice: The website called Pediaa might have its maintenance going on because of which the server seems down.So please believe my mentioned words, they have been exactly copied.