Чем отличается DisplayPort 1.4 от DisplayPort 1.4a ? (На новых видюхах Nvidia DisplayPort 1.4a)

В версии 1.4a обновлена VESA Display Stream Compression (DSC) до версии 1.2a. Версия DSC 1.2a имеет следующие изменения:
Added proposed changes from the following DSC v1.2 SCRs:
• Applied SCR# DSC 1.2 RGB 16bpc clarification
• Section 6.1 and Section 7.7 – Corrections to Co and Cg when
bits_per_component is equal to 16
• Applied SCR# DSC 1.2 QP Restriction in 1.1 YCbCr Mode
• Table 4-3 – Updated range_max_qp description
• Added qp-related text to Table E-4/Table E-5 introduction
• Applied SCR# DSC 1.2 4:2:2 mode specification typos
• Section 3.10.1 – Corrected last paragraph
• Section 6.5.3.1 – Corrected weightedSad equation (changed + to *)
• Applied SCR# Change on rules for slice_height/picture_height in 4:2:2 and 4:2:0
• Table 4-1 – Revised last two paragraphs of slice_height and slice_width
definitions
• Applied SCR# DSC 1.2 4:2:0 prediction and RC bug fixes SCR v4
• Section 1.3, Section 3.4, Section 6.4.1, Section 6.5.1, Section 6.8.4 –
Added Native 4:2:0 mode-related clarifications
• Table 1-1 – Added DSC v1.2a-supported modes, removed DSC v1.2 support
for Native 4:2:0 mode
• Applied SCR# DSC 1.2 alternative encoder ICH selection SCR v5
• Section 6.5.3.3 – Added
• Applied SCR# DSC 1.2 YCbCr QP map spec typo fix SCR
• Section 6.8.6 – Revised second paragraph
• Applied SCR# DSC 1.2 C model max QP check SCR v2
• Adds new paragraph to Table E-4/Table E-5 introduction
Подробнее здесь: https://glenwing.github.io/docs/VESA-DSC-1.2a.pdf

По всей видимости, 1.4a - это и есть 1.4.