Taña ya ha aportado la fuente que yo manejaba:
http://www.ljmu.ac.uk/NSP/NSP_Docs/Guidance_for_Tutors_-_tra...
Todo se explica allí

DC = Deferred Consideration
"Consideration" aquí quiere decir "evaluación":

"Exceptionally, if a pre-scheduled event will prevent a student from attempting a module assessment, the student may request that consideration of his/her performance is deferred until the subsequent assessment opportunity. (Examples of circumstances where this procedure applies could include events such as: jury service, medical treatment, military service etc)."
http://www.ljmu.ac.uk/corporate/SPR/99506.htm

Es decir, que el examen u otra evaluación se aplaza.
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PMC = Personal Mitigating Circumstances

En el ámbito legal, son atenuantes, pero aquí se refiere a problemas personales que repercuten en el rendimiento del estudiante y que pueden tenerse presentes a la hora de evaluarlo. He estado dando vueltas a cómo expresarlo y he optado por "problemas personales relevantes".

Para detalles de qué son estas "circunstancias", ver
http://www.ljmu.ac.uk/corporate/SPR/SPR_Docs/PMC-guidancenot...
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INV = Invalid: se rechaza la petición de que se aplace la evaluación o que se revise la nota en vista de los problemas aducidos.

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Note added at 53 mins (2011-11-22 19:45:09 GMT)
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He aquí una explicación de las PMC, de la fuente citada arriba:

"What are Personal Mitigating Circumstances?

The University acknowledges that there may be occasions when a student’s performance in assessment may be severely affected by unforeseen or unexpected personal circumstances. Such events include sudden acute illness or close personal bereavement. [It does not include circumstances that arise from minor ailments such as a cold, or circumstances that arise as a result of foreseeable circumstances, such as booking a holiday during an assessment period, or long term medical conditions / disabilities (UMF Regs. Appendix B (2) refers]."