In 278.sld you have

     ((library (srfi 144))
      (import (only (srfi 144)
                    flonum
                    fl-greatest
                    fl-epsilon
                    fladjacent
                    fl-pi/2
                    fl-pi/4
                    make-flonum
                    flexponent
                    flasinh
                    flsinh
                    flcosh
                    flatanh
                    fllog1+))
      (begin (define fl-least-normal
               (- 1.0 (fladjacent 1.0 0.0)))))

I think that in 278.sld the definition you give of fl-least-normal is
the value of fl-epsilon.

The Gambit test suite has minimal unit tests for some routines in this
SRFI in this directory:

https://github.com/gambit/gambit/tree/master/tests/unit-tests/03-number

They use the following definitions:

;;; Naive, but correct, definitions of inverse trigonometric and
;;; hyperbolic functions in terms of log and sqrt.

(define (test-atanh z)
   (declare (standard-bindings) (generic))
   (* 1/2 (- (log (+ 1 z)) (log (- 1 z)))))

(define (test-atan z)
   (declare (standard-bindings) (generic))
   (/ (test-atanh (* +i z)) +i))

(define (test-asinh z)
   (declare (standard-bindings) (generic))
   (log (+ z (sqrt (+ (* z z) 1)))))

(define (test-asin z)
   (declare (standard-bindings) (generic))
   (/ (test-asinh (* +i z)) +i))

(define (test-acos z)
   (declare (standard-bindings) (generic))
   (- (macro-inexact-+pi/2) (test-asin z)))

(define (test-acosh z)
   (declare (standard-bindings) (generic))
   (* 2 (log (+ (sqrt (/ (+ z 1) 2)) (sqrt (/ (- z 1) 2))))))

Brad