Turns out that beyond just CDA-20878, we have quite a few other instances of C-CDA reusing the same codes across different templates. Here's the list I turned up:

46241-6: HospitalAdmissionDiagnosis, AdmissionDiagnosisSection
42346-7: AdmissionMedication, AdmissionMedicationsSectionEntriesOptional
33999-4: ProblemStatus, AllergyStatusObservation
85847-2: CareTeamsSection, CareTeamMemberAct
86744-0: CareTeamTypeObservation, CareTeamOrganizer
8648-8: HospitalCourseSection, CourseofCareSection
11535-2: DischargeDiagnosisSection, HospitalDischargeDiagnosis
10183-2: DischargeMedication, DischargeMedicationsSection
75310-3: HealthConcernsSection, HealthConcernAct
59769-0: PostprocedureDiagnosis, PostprocedureDiagnosisSection
10219-4: PreoperativeDiagnosis, PreoperativeDiagnosisSection

We should probably better differentiate those from one another. There were also a few others that are likely okay:

I think it's okay to reuse CONC and ASSERTION:

CONC: AllergyConcernAct, ProblemConcernAct
ASSERTION: DeceasedObservation, LongitudinalCareWoundObservation, ReactionObservation, PregnancyObservation, NumberofPressureUlcersObservation, PatientReferralAct, PreconditionforSubstanceAdministration, AllergyIntoleranceObservation, SubstanceOrDeviceAllergyIntoleranceObservation, WoundCharacteristic, FamilyHistoryDeathObservation, ProgressTowardGoalObservation

Reusing the same SNOMED code for planned vs. actual interventions seems okay too.

362956003: PlannedInterventionAct, InterventionAct

And the Payers one we already addressed in CDA-20878:

48768-6: PlannedCoverage, PayersSection