On second thought I may have this backwards. The latter books - 62-90
(leaving aside 91-93) might be the original book and 1-61 the latter
addition.
al-Bukhari is said, in the standard sources (I do not know with what
authority), is said have been a Shafi'i lawyer and to have written his
collection to provide his fellow lawyers with a convenient handbook of
hadiths for use in their cases. This makes sense.
But the last third of the collection is what really is addressed to
that question. Consider the titles of the books:
62. Wedlock
63. Divorce
64. Provision
65. Food
66. 'Aqiqa
67. Slaughter
68. Adahi
69. Drink
70. Patients
71. Medcine
72. Dress
73. Adab
74. Asking Permission
75. Invocation
76. al-Riqaq
77. al-Qadar
78. Oaths
79. Expiation
80. Inheritance
81. Hudud.
82. Apostates
83. Blood Money
84. Reverters
85. Coercion
86. Tricks
87. Dreams
88. Afflictions
89. Judgment
90. Wishes
This seems much more in accord with what a lawyer would need to know
about than the first two-thirds of the collection with one notable
exception - business law. Business law is in the following books
34. Buying and Selling
35. al-Salam
36. Renting
37. Debts
38. Agency
39. Agriculture
40. Water
41. Loans
42. Luqata
43. Oppression
44. Partnership
45. Mortgages
46. Manumission
47. Gifts
48. Witnesses
49. Peace-making
50. Conditions
51. Wills
These also seem to relate directly to a lawyer's needs.
Have I perhaps stumbled over a divide in practice among the lawyers of
the day? Were there two communities of lawyers - those specialized in
business law and those in general practice?