ಈಪೊತ್ತು (present tense) is unique to ಇರು as a nerevaesaka (auxiliary). Regular verbs have only past/non-past. The present forms ಇದ್ದಾನೆ, ಇದ್ದಾಳೆ etc. mark "currently in a state of being" — distinct from ongoing action (ಮುಂಬೊತ್ತು) or completed past (ಹಿಂಬೊತ್ತು).
ಇದೆ / ಇವೆ — the 3rd person neuter present forms are maximally irregular: the expected *ಇದ್ದದೆ / *ಇದ್ದವೆ are replaced by these short forms, reflecting a different historical origin.
ಇರದ — only one negative participial survives in ಇರು's own paradigm, used in constructions like ಮಾಡಿರದ ಕೆಲಸ (work not done). The other three negative non-finites use ಇಲ್ಲ.
Why not ಇರದೆ (irade)? — ಇರದೆ is the morphologically expected negative converb (stem + -ade), and it does appear in formal/literary Kannada: "ಅಲ್ಲಿ ಇರದೆ ಹೋದ" (went without staying there). In colloquial modern Kannada however, ಇಲ್ಲದೆ has displaced it almost entirely. Bhat's 42-count therefore treats this slot as suppletive. ಇರದ (participial) survives because it has a distinct literary niche — "ಇರದ ದೇವರು" — whereas the converb has no such anchor.
Why not ಇರುವೆ (iruve)? — ಇರುವೆ (iru + linking -v- + 1sg -e) is a valid literary and formal form; its paradigm-mates run: ಇರುವೆ, ಇರುವೆವು, ಇರುವಿರಿ… These come from an older -uva- participial-based conjugation found in classical poetry and formal registers. Bhat's §5.1.1 uses the -utt- non-past marker throughout (same as all regular verbs — ಮಾಡುತ್ತೇನೆ, ಕೇಳುತ್ತೇನೆ), giving irutteNe for 1sg. The -uve alternates belong to a parallel literary paradigm and are not double-counted in the 42.
Why not ಇರಿಹನು (irihanu), ಇರಲಾರೆ (iralAre), and similar? — These are compound verb forms (ಕೂಡಿಕೆ ರೂಪ), not entries in the simplex paradigm. ಇದ್ದಿಹನು = converb ಇದ್ದು + emphatic/concessive particle ಹನು, a clitic that attaches to any converb of any verb ("having been — I assert / contrary to expectation"). ಇರಲಾರೆ = purpose converb ಇರಲು + defective auxiliary ಆರು (1sg) = "I cannot be / am unable to be." Bhat's 42 captures only simplex forms (one suffix → one stem). Compound forms are productive by multiplication; the vector verb (ನೆರವೆಸಕ) system — ಇರು itself as aspectual auxiliary — is covered in Book 32. The same principle applies to all verbs: mADihanu, mADalAre etc. are likewise ಕೂಡಿಕೆ ರೂಪ.
As vector verb (Book 32): ಇರು encodes aspectual continuation — ಮಾಡುತ್ತಿದ್ದೆ (was doing) = ಮಾಡು + simultaneous converb + ಇರು past, drawing on the ಈಪೊತ್ತು/ಹಿಂಬೊತ್ತು distinction.